Method and apparatus for compression, method and apparatus for decompression, compression/decompression system, record medium

ABSTRACT

On a compression side, from an inputted analog signal  101 , points  102   a  to  102   f  where a differential absolute value is at a predetermined value or smaller are detected as sample points, and a pair of discrete amplitude data on the sample points and timing data indicative of a time interval between sample points is obtained as compressed data. On an expansion side, amplitude data and timing data that are included in the compressed data are used to obtain expansion data by determining interpolation data for interpolating two pieces of amplitude data, based on the two pieces of amplitude data on two successive sample points and timing data therebetween. Thus, when a signal on a time base is compressed and expanded, the operation can be performed on a time base without frequency conversion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to method and apparatus for compression,method and apparatus for decompression, compression/decompressionsystem, and record medium, particularly to a method for compression anddecompression a continuous analog signal or digital signal.

2. Description of the Related Art

Conventionally, when transmitting and storing a signal such as a picturesignal and an aural signal that has a large amount of information, asignal has been compressed and expanded in order to reduce an amount oftransmitted information, increase a storing time of a storage medium,and so on. Generally, when an analog signal is compressed, an analogsignal is initially sampled according to a predetermined samplingfrequency and is digitized, and compression is performed on the obtaineddigital data.

For example, in the case of compression on a picture signal and an auralsignal, a method is used in which compression is performed on afrequency region after original data is processed using a conversionfilter on a time base-frequency axis such as DCT(Discrete-Cosine-Transform). DPCM (Differential Pulse Code Modulation),which is frequently used as a method of compression an aural signal fora telephone line, is used with the same intention. Additionally, theDPCM compression is a method for coding a difference of adjacent samplevalues when a waveform is sampled.

Further, as a method for performing time/frequency conversion, a methodusing a sub-band filter and MDCT (Modified Discrete Cosine Transform) isalso available. As a coding method using such a method, MPEG (MovingPicture Image Coding Experts Group) audio is applicable.

Further, the most widely used picture compression system is generallyknown as the MPEG standard.

Data compressed by the above compression method is basically expandedaccording to reversed operations of the same compression method.

Namely, after compressed digital data is converted from a signal of afrequency region to a signal of a time region by frequency/timeconversion, predetermined decompression operations are carried out toreproduce original digital data. And then, the original data obtainedthus is subjected to digital-analog conversion if necessary and isoutputted as an analog signal.

However, in the above conventional compression and decompression method,a signal on a time base is converted to a signal on a frequency axisbefore compression. Hence, operations such as time/frequency conversionfor compression and frequency/time conversion for expansion arenecessary. Therefore, the operations are complicated and theconfiguration for realizing the operations becomes extremelycomplicated. This problem has caused not only a longer processing timefor compression and expansion but also difficulty in achieving a smallerdevice.

Moreover, generally in the case of compression and expansion of data, itis important to consider how to improve the quality of reproduced datawhile improving its compressibility. However, in the above conventionalcompression and decompression method, when a compressibility of apicture signal and an aural signal is increased, an image and voicereproduced by decompression compressed data are degraded in quality. Incontrast, when importance is placed on the quality of a reproduced imageand reproduced voice, a picture signal and an aural signal decreases incompressibility. Therefore, it has been extremely difficult to achieveboth of an increased compressibility and improved quality of reproduceddata.

The present invention is devised to solve the above problems and aims tosimplify the compression and decompression operations for a signal so asto shorten a processing time and to simplify the configuration forrealizing the operations.

Also, another object of the present invention is to provide a newcompression and decompression method for increasing compressibility andimproving quality of reproduced data.

Furthermore, another object of the present invention is to more readilyperform compression and expansion without using a table.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, on a compression side ofthe first invention, a signal to be compressed is sampled at a timeinterval of a point where a differential absolute value is at apredetermined value or smaller, a pair of discrete amplitude data oneach sample point and timing data indicative of a time interval betweensample points is obtained as compressed data.

Here, a signal to be compressed may be oversampled, and the oversampleddata may be sampled at a time interval of a point where a differentialabsolute value is at a predetermined value or smaller. Further, on theoversampled data, the operation for generating average value data ofsuccessive sample values may be further performed.

Moreover, on an expansion side of the first invention, regardingcompressed data composed of a pair of amplitude data on predeterminedsample points extracted from a signal to be compressed and timing dataindicative of a time interval between sample points, amplitude data onsuccessive sample points and timing data therebetween are used to obtaininterpolation data for interpolating pieces of amplitude data having atime interval indicated by the timing data. Thus, expansion data isobtained.

Here, a sampling function obtained from two pieces of amplitude data ontwo successive sample points and timing data therebetween may be used toobtain interpolation data for interpolating the two pieces of amplitudedata.

According to the first invention configured thus, when a signal iscompressed on a time base, the operation can be performed on a time basewithout performing time/frequency conversion on a frequency axis.Besides, when data compressed thus is expanded as well, the operationcan be performed on a time base. Therefore, it is possible to simplifycompression and expansion, to shorten an operating time, and to simplifythe configuration for the operations. Also, when compressed data istransmitted from the compression side and is reproduced on the expansionside, a simple interpolating operation on a time base can sequentiallyprocess and reproduce compressed data inputted to the expansion side,thereby realizing real-time operations.

Besides, in the present embodiment, only data on sample points ofsampling points can be obtained as compressed data, thereby achievinghigh compressibility. The sample points are equivalent to inflectedpoints in a signal to be compressed, and the sample points include allminimum points required for reproducing original data by aninterpolating operation on the expansion side. Therefore, it is possibleto obtain high-quality reproduced data with higher reproducibility oforiginal data.

Further, on the compression side of the second invention, digital dataof a basic waveform corresponding to values of inputted n pieces ofdiscrete data is synthesized by oversampling and a moving averageoperation or a convoluting operation so as to obtain digitalinterpolation values for the discrete data. Thereafter, the digitalinterpolation values are sampled at a time interval of a point having aminimum differential absolute value, and a pair of discrete amplitudedata on sample points and timing data indicative of a time intervalbetween sample points is obtained as compressed data.

Moreover, on the expansion side of the second invention, by usingamplitude data and timing data that are included in compressed data,based on two pieces of amplitude data on two successive sample pointsand timing data therebetween, interpolation data for interpolating thetwo pieces of amplitude data is determined so as to obtain expansiondata.

According to the second invention configured thus, when data iscompressed on a time base, the operation can be performed on a time basewithout performing time/frequency conversion on a frequency axis.Besides, when data compressed thus is expanded as well, the operationcan be performed on a time base. Therefore, it is possible to simplifycompression and expansion, to shorten an operating time, and to simplifythe configuration for the operations. Also, when compressed data istransmitted from the compression side and is reproduced on the expansionside as well, a simple interpolating operation on a time base cansequentially process and reproduce compressed data inputted to theexpansion side, thereby realizing real-time operations.

Besides, only data on sample points of sampling points can be obtainedas compressed data, thereby achieving high compressibility. The samplepoints are equivalent to inflected points in a signal to be compressed,and the sample points include all minimum points required forreproducing original data by an interpolating operation on the expansionside. Therefore, it is possible to obtain high-quality reproduced datawith higher reproducibility of original data.

Additionally, according to the second invention, when an interpolationvalue is obtained by performing oversampling and convolution on digitaldata, only values of a limited number of pieces of discrete data need tobe considered for determining a certain interpolation value, therebypreventing a censoring error. Thus, an interpolation value can beobtained accurately. Therefore, regarding data reproduced on theexpansion side when compression is performed using the interpolationvalue, it is possible to improve reproducibility to original data beforecompression.

Besides, on the compression side of the third invention, inputteddigital data is differentiated, a point where a differential valuechanges in polarity is detected as a sample point, and digital datarounded by a predetermined value is obtained as discrete compressedamplitude data on sample points. A pair of compressed amplitudedifference data, which is obtained by computing a difference betweenpieces of the compressed amplitude data, and timing data indicative of atime interval between sample points is obtained as compressed data.

Further, on the expansion side of the third invention, the compressedamplitude difference data, which is oversampled by even-numbered times,is subjected to multiple integral, and a moving average operation isperformed on the integral value. A moving average value obtained thusand timing data is used to obtain square-law interpolation data, whichinterpolates pieces of amplitude data on sample points having a timeinterval indicated by the timing data, as expansion data.

In another aspect of the third invention, on the compression side,inputted digital data is rounded by a first value, the digital datarounded by the first value is differentiated and a point where adifferential value changes in polarity is detected as a sample point.Digital data rounded by a second value, which is larger than the firstvalue, is obtained as discrete compressed amplitude data on samplepoints.

In another aspect of the third invention, on the compression side, thecompressed amplitude difference data and the timing data are convertedto variable-length block data.

In another aspect of the third invention, on the expansion side, thecompressed amplitude difference data oversampled by even-numbered timesis reversed in sign at an intermediate position of each section betweensample points, the section being indicated by the timing data. Datastrings obtained thus are subjected to multiple integral.

In another aspect of the third invention, on the expansion side,multiple integral and a moving average operation are performed in eachsection between sample points on the compressed amplitude differencedata oversampled by even-numbered times.

According to the third invention configured thus, when a signal on atime base is compressed, the operation can be performed on a time basewithout performing time/frequency conversion on a frequency axis.Besides, when data compressed thus is expanded as well, the operationcan be performed on a time base. Therefore, it is possible to simplifycompression and expansion, to shorten an operating time, and to simplifythe configuration for the operations. Also, during expansion, a simplesquare-law interpolating operation on a time base can sequentiallyprocess and reproduce inputted compressed data without using tableinformation, thereby realizing real-time operations.

Furthermore, according to the third invention, compressed data can begenerated from only few pieces of discrete data that include anamplitude data value on a sample point where digital data has adifferential value changing in polarity and a timing data valueindicative of a time interval of sample points. Besides, since amplitudedata on sample points is rounded by a predetermined value, it ispossible to shorten a data length of amplitude data by several bits perword, thereby largely reducing an amount of data. Additionally, in thethird invention, rounded amplitude data is not used as compressed datadirectly but difference data is further determined as compressed data.Hence, it is possible to further reduce the number of bits required forcompressed data, thereby reducing an amount of data.

Moreover, according to other characteristics of the third invention,compressed amplitude difference data and timing data that are obtainedthus are encoded to variable-length block data as final compressed data.Thus, compressibility can be further increased.

Besides, according to the third invention, an inflection point existingin a signal to be compressed is detected as a sample point, andcompressed data includes all minimum points required for reproducingoriginal data by an interpolating operation on the expansion side.Therefore, it is possible to increase reproducibility of original data,thereby obtaining high-quality reproduced data.

Additionally, according to another characteristic of the thirdinvention, digital data rounded by a suitable value is differentiated todetect a sample point. Hence, it is possible to prevent positions ofnoise components and unnecessary signal components from being detectedas sample points, thereby positively detecting only correct positions assample points. Therefore, as for expansion data reproduced on theexpansion side, it is possible to improve reproducibility of originaldata before compression.

Further, according to another characteristic of the third invention,compressed amplitude difference data oversampled by even-numbered timesis reversed in sign at an intermediate position of each section betweensample points. Hence, when multiple integral and a moving averageoperation are performed on data strings reversed in sign, it is possibleto compensate for a rounding error on the compression side and toreproduce a digital waveform having more smoothly changing amplitudevalues.

Besides, according to another characteristic of the third invention, onthe expansion side, multiple integral is performed in each sectionbetween sample points. Thus, it is possible to eliminate an accumulativeerror caused by integral, thereby reproducing a digital waveform moreaccurately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a compression method of Embodiment 1;

FIG. 2 is a diagram for explaining an decompression method of Embodiment1;

FIGS. 3A and 3B are diagrams showing an interpolating principle of thepresent embodiment by taking out the section between time T1 and T2 ofFIG. 2;

FIG. 4 is a diagram showing an example of a sampling function;

FIG. 5 is a diagram showing the relationship between pieces of discretedata and interpolation values therebetween;

FIG. 6 is a diagram for explaining an interpolating equation, which is aspecific example of data interpolation on the expansion side;

FIG. 7 is a diagram showing the results of performing oversampling andconvolution on time T1 and T2 of FIG. 2;

FIG. 8 is a diagram showing another results of performing oversamplingand convolution;

FIG. 9 is a block diagram showing an example of the configuration of acompression apparatus according to Embodiment 1;

FIG. 10 is a block diagram showing an example of the configuration of anaverage value interpolation data generating section shown in FIG. 9;

FIG. 11 is a block diagram showing an example of the configuration of atiming synthesizer shown in FIG. 9;

FIG. 12 is a block diagram showing an example of the configuration of andecompression apparatus according to Embodiment 1;

FIG. 13 is a block diagram showing an example of the configuration of acompression apparatus according to Embodiment 2;

FIG. 14 is a block diagram showing an example of the configuration of andecompression apparatus according to Embodiment 2;

FIG. 15 is a diagram showing a digital basic waveform used in Embodiment2;

FIG. 16 is a diagram for explaining an example of the operation ofoversampling and convolution according to Embodiment 2;

FIG. 17 is a diagram showing a function generated from the digital basicwaveform of FIG. 15;

FIG. 18 is a diagram showing an example of the configuration of anoversampling circuit shown in FIG. 13;

FIG. 19 is a diagram showing an example of digital data inputted to thecompression apparatus of Embodiment 2;

FIG. 20 is a diagram showing an example of data outputted by passingdigital data of FIG. 19 through an oversampling circuit of FIG. 13;

FIG. 21 is a diagram showing an example of the configuration of adifferentiator shown in FIG. 13;

FIG. 22 is a diagram showing an example of data outputted by passingoversampled data of FIG. 20 through the differentiator of FIG. 13;

FIG. 23 is an explanatory drawing showing the operation for the casewhere equal differential absolute values appear successively;

FIG. 24 is a block diagram showing an example of the configuration fordetecting a sample point by double differentiation;

FIG. 25 is a diagram showing an example of compressed data outputted bypassing the oversampled data of FIG. 20 through a compressed datagenerating section of FIG. 13;

FIGS. 26A and 26B are diagrams for explaining another example of datainterpolation on the expansion side;

FIG. 27 is a diagram showing an example of expansion data outputted froman expanding section of FIG. 14 when expansion is performed on thecompressed data of FIG. 25;

FIG. 28 is a block diagram showing an example of the configuration of acompression apparatus according to Embodiment 3;

FIG. 29 is a diagram for explaining the operating principles of a timinggenerator and an amplitude generator of FIG. 28;

FIG. 30 is a block diagram showing an example of the configuration ofthe timing generator shown in FIG. 28;

FIG. 31 is a diagram showing a detailed example of the configuration ofa part for generating a timing pulse;

FIG. 32 is a diagram for explaining an example of an actual compressionoperation performed by the compression apparatus of Embodiment 3;

FIGS. 33A and 33B are diagrams showing an example of the configurationof serial compressed block data according to Embodiment 3;

FIG. 34 is a block diagram showing an example of the configuration of andecompression apparatus according to Embodiment 3;

FIG. 35 is a diagram showing a detailed example of the configuration ofa square-law interpolation data generating section of FIG. 34;

FIG. 36 is a diagram for explaining an example of an actualdecompression operation performed by the decompression apparatus ofEmbodiment 3; and

FIG. 37 is a diagram showing an example of original data beforecompression and expansion data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be discussed inaccordance with the accompanied drawings.

(Embodiment 1)

FIG. 1 is a diagram for explaining a compression method of Embodiment 1and showing an example of an input analog signal to be compressed.Further, FIG. 2 is a diagram for explaining an decompression method ofthe present embodiment.

First, referring to FIG. 1, the compression operation will be discussed.In the present embodiment, points 102 a to 102 f (hereinafter, referredto as sample points), on which differential absolute values (inclinationof a signal) are at a predetermined value including “0” or smaller, aredetected from an input analog signal 101. And then, digital data values,which are obtained by performing analog-digital conversion on amplitudeof the sample points 102 a to 102 f, and timing data values, which areindicative of time intervals of the sample points 102 a to 102 f, areobtained. A pair of the amplitude data value and the timing data valueis transmitted or recorded as compressed data.

In the example of FIG. 1, “7, 3, 9, 1, 6, 3” are obtained as digitalamplitude data values on the sample points 102 a to 102 f, and “5, 7, 3,3, 3” are obtained as timing data indicative of time intervals betweentime T1 and T2, time T2 and T3, time T3 and T4, time T4 and T5, and timeT5 and T6 of the sample points 102 a to 102 f. Here, numbers shown astiming data indicate the number of clocks that depends upon a samplingfrequency.

At time T1, an amplitude data value “7” on the sample point 102 a and atiming data value (not shown), which is indicative of a time intervalfrom when a sample point (not shown) is previously detected, areobtained. Thus, a pair of the data values is transmitted or recorded ascompressed data of time T1.

Next, at time T2 when the sample point 102 b is detected, a timing datavalue “5”, which is indicative of a time interval from time T1 when thesample point 102 a is previously detected, and an amplitude data value“3” on the sample point 102 b are obtained. Thus, a pair of the datavalues (5, 3) is transmitted or recorded as compressed data of time T2.

Next, at time T3 when the sample point 102 c is detected, a timing datavalue “7”, which is indicative of a time interval from time T2 when thesample point 102 b is previously detected, and an amplitude data value“9” on the sample point 102 c are obtained. Thus, a pair of the datavalues (7, 9) is transmitted or recorded as compressed data of time T3.

In a similar manner, as compressed data of time T4, T5, and T6, (3, 1),(3, 6), and (3, 3), which are pairs of timing data values and amplitudedata values, are transmitted or recorded. The timing data values areindicative of time intervals between time T3 and T4, time T4 and T5, andtime T5 and T6, and the amplitude data values are detected on the samplepoints 102 d, 102 e, and 102 f at time T4, T5, and T6.

Subsequently, referring to FIG. 2, the following will discuss andecompression operation of data compressed as shown in FIG. 1. When theinput analog signal 101 is compressed according to the method of FIG. 1,a numeral series of (*, 7), (5,3), (7,9), (3,1), (3,6), and (3, 3) isobtained as compressed data. Here, * indicates that no value is shown inFIG. 1. Compressed data is inputted to an expansion side in the aboveorder.

On the expansion side, data of a waveform a1 is generated by aninterpolating operation from two data values of a firstly inputtedamplitude data value “7” and a timing data value “5”. Next, data of awaveform a2 is generated by interpolation from two data values of theabove timing data value “5” and a subsequently inputted amplitude datavalue “3”.

And then, from two data values of the above amplitude data value “3” anda subsequently inputted timing data value “7”, data of a waveform b2 isgenerated by interpolation. Further, from the above timing data value“7” and a subsequently inputted amplitude data value “9”, data of awaveform b1 is generated by interpolation. In a similar manner, frompairs of sequentially inputted amplitude data values and timing datavalues, data of waveforms c1, c2, d2, d1, e1, and e2 is generatedsequentially.

The above operation produces a digital signal (upper stage of FIG. 2)having the waveforms a1, b1, c1, d1, and e1 continuously formed, and adigital signal (lower stage of FIG. 2) having the waveforms a2, b2, c2,d2, and e2 formed continuously. And then, the two digital signalsproduced thus are added to each other and are subjected todigital-analog conversion. Hence, the original analog signal of FIG. 1is reproduced.

FIGS. 3A and 3B show a section between time T1 and T2 of FIG. 2. FIG. 3Ashows the two waveforms a1 and a2 before addition. FIG. 3B shows asynthetic waveform a1+a2 reproduced by addition.

In FIG. 3A, reference numeral D1 denotes an amplitude data value (“7” inthe example of FIG. 2) at time T1, reference numeral D2 denotes anamplitude data value (“3” in the example of FIG. 2) at time T2,reference character T denotes a timing data value (“5” in the example ofFIG. 2) indicative of a time interval between time T1 and T2, andreference character t denotes arbitrary timing between time T1 and T2.

As shown in FIG. 3A, data of the waveform a1 is generated byinterpolation using an amplitude data value D1 at time T1 and a timingdata value T indicative of a time interval between time T1 and T2 whilean arbitrary timing t between time T1 and T2 acts as a variable, thatis, while a value of timing t is incremented one by one according to aclock based on a sampling frequency.

Moreover, data of the waveform a2 is generated by interpolation using anamplitude data value D2 at time T2 and a timing data value T indicativeof a time interval between time T1 and T2 while the timing t similarlyacts as a variable.

And then, pieces of data of the waveforms a1 and a2 generated thus areadded to each other while the timing t acts as a variable. Hence, awaveform of FIG. 3B is synthesized. In this manner, the original analogsignal before compression can be reproduced.

The following will discuss a principle of reproducing the originalanalog signal by the decompression operation using the aboveinterpolation.

In general, in order to obtain a continuous analog signal from discretedigital data, interpolation is performed between pieces of digital datainputted in a discrete manner and a sampling frequency is increasedartificially. Such data interpolation is normally performed using apredetermined sampling function.

FIG. 4 shows an example of a sampling function. In the example of FIG.4, a value is set at “1” only on a sampling point of t=0, and values areall set at “0” on other sampling points (t=±1, ±2, ±3, ±4, . . . )having regular intervals.

FIG. 5 is a diagram for explaining a typical operation of datainterpolation using such a sampling function. In FIG. 5, it is assumedthat sampling points t1, t2, t3, and t4 at regular intervalsrespectively have discrete data values of Y(t1), Y(t2), Y(t3), and Y(t4)and, for example, an interpolation value y is determined, whichcorresponds to a predetermined position to (distance a from t2) betweenthe sampling points t2 and t3.

In general, when an interpolation value y is obtained using a samplingfunction, a value of a sampling function on an interpolating position t0is obtained for each of provided pieces of discrete data, and aconvoluting operation is carried out using the values. To be specific,each of the sampling points t1 to t4 is caused to have an equal peakheight at the center of a sampling function. A sampling function value(indicated by x) is computed for each of the sampling points at theinterpolating position t0, and all the values are added.

Such interpolation is carried out while the interpolating position to ismoved sequentially with the passage of time (in accordance withincrement of a sampling clock). Thus, an interpolation value y (t0),which varies continuously, is computed in a sequential manner. Hence, itis possible to obtain a continuous analog signal for connecting piecesof discrete data smoothly.

The present embodiment applies such data interpolation. Namely, as shownin FIG. 3A, the waveform a1 is obtained, which forms a part of asampling function having a value other than “0” on a first sample point(time T1), from an amplitude data value D1 (=7) and a timing data valueT (=5) that have already been inputted at time T2. Further, the waveforma2 is obtained, which forms a part of a sampling function having a valueother than “0” on a second sample point (time T2), from an amplitudedata value D2 (=3) and a timing data value T (=5).

And then, the values of the waveforms a1 and a2 are added on eachinterpolating position t, which sequentially moves with the passage oftime. Thus, it is possible to obtain a continuous analog signal forconnecting discrete data D1 and D2 smoothly.

Besides, the present embodiment describes that pieces of data of thewaveforms a1 and a2 are added to each other after they are obtained. Itis also possible to obtain a synthetic waveform at one time by using apredetermined equation and so on because data for generating andsynthesizing the waveforms a1 and a2 is all obtained at time T2.

Incidentally, in the present embodiment, as shown in FIG. 1, discretedata serving as compressed data is obtained by sampling the input analogsignal 101, which varies smoothly, on the compression side at timeintervals of points on which differential absolute values are at apredetermined value or smaller. Therefore, the sample points on whichdiscrete data is obtained are not always evenly spaced and the intervalsbecome irregular in many cases (in the example of FIG. 1 as well, thesample points are unevenly spaced in “5, 7, 3, 3, 3”) Hence, on theexpansion side of FIG. 2, for example, when an interpolation valuebetween time T1 and T2 is computed, as shown in FIG. 3, the aboveconvoluting operation is performed by using only sampling functions a1and a2 at a time interval between the sample points of the time T1 andT2. Other sampling functions b1, b2, c1, c2, d1, d2, e1, and e2 havingdifferent time intervals between sample points are not taken intoconsideration when the convoluting operation is carried out.

Moreover, for example, when an interpolation value is computed betweentime T2 and T3, a convoluting operation is performed by using onlysampling functions b1 and b2 at a time interval (=7) between samplepoints of time T2 and T3. Other sampling functions a1, a2, c1, c2, d1,d2, e1, and e2, which have different time intervals between samplepoints, are not taken into consideration when the convoluting operationis carried out. This holds true when interpolation values are obtainedbetween other sample points.

Namely, in the compression/decompression system of the presentembodiment, on the compression side, the input analog signal 101 varyingsmoothly is sampled at irregular time intervals having differentialabsolute values at a predetermined value or smaller. Thus, discreteamplitude data values and timing data values indicative of irregulartime intervals are obtained as compressed data. Further, on theexpansion side, according to the amplitude data values and the timingdata values in compressed data, a continuous analog signal is generated,which connects pieces of discrete data at time intervals as irregular asthe compression side, by interpolation using the above samplingfunctions.

Next, the following will discuss a specific example of the above datainterpolation. As described above, for example, when an interpolationvalue is obtained between time T1 and T2, only the sampling functions a1and a2 are used, which are obtained from amplitude data values in timeT1 and T2 and a timing data value indicative of a time interval betweentime T1 and T2. Namely, data required for computing an interpolationvalue on each interpolating position t between time T1 and T2 is allobtained at time T2, so that it is possible to reproduce the originalanalog signal shown in FIG. 3B at this moment.

Therefore, in the present embodiment, every time two amplitude datavalues D1 and D2 and a timing data value T indicative of a time intervaltherebetween are obtained for each discrete time of T1 to T6, aninterpolation value is computed by using the data values according to aninterpolating equation, which will be discussed later. Hence, theoriginal analog signal is reproduced sequentially. FIG. 6 is a diagramfor explaining the interpolating equation.

As shown in FIG. 6, an interpolation value between two sample pointshaving amplitude data values of D1 and D2 can be represented by afunction in which two quadratic functions x1 and x2 regarding aninterpolating position t are connected at an intermediate point. Namely,in the present embodiment, a part between two sample points is dividedinto a first half and a second half, and interpolation values thereofare respectively computed using the quadratic functions x1 and x2.

A timing data value T, which is a time interval between the samplepoints, may be an odd number or an even number. In the case of an oddnumber, an interpolating position t may not be set at an intermediatepoint. Therefore, in the present embodiment, an obtained timing datavalue is always set at an even number by performing double oversamplingupon compression. Namely, the five timing data values “5,7,3,3,3” ofFIG. 1 are transmitted or stored actually as values of “10,14,6,6,6” bydouble oversampling. In FIG. 6, a time interval between the samplepoints is represented by 2T obtained after oversampling.

In FIG. 6, the two quadratic functions x1 and x2 are respectivelyrepresented by the following equations.

x1=D1+at ²  (1)

x2=D2−a (t−2T)²  (2)

Moreover, since the functions x1 and x2 are connected at theintermediate point T of the successive sample points, the followingequation is established.

x1=x2 (t=T)  (3)

Here, when equations (1) and (2) are substituted for equation (3), thefollowing equation is established.

D1+aT ²=D2−aT ²  (4)

When equation (4) is solved for a, the following equation isestablished.

a=−(D1−D2)/2T²  (5)

Therefore, the following equations are established by substitutingequation (5) for equations (1) and (2).

x1=D1−{(D1−D2)/2T² } t ²  (6)

x2=D2+{(D1−D2)/2T²}(2T−t)²  (7)

Namely, the original analog signal can be reproduced by performingequations (6) and (7) while an interpolating position t serves as avariable, which is sequentially incremented according to a clock of adoubled sampling frequency. In the present embodiment, such aninterpolating operation is performed sequentially every time a signalline composed of an amplitude data value and a timing data value isinputted at each of discrete time T1 to T6.

Namely, in the example of FIG. 2, when amplitude data values on thesamples points at time T1 and T2 and a timing data value therebetweenare inputted, an interpolating operation is performed between the samplepoints so as to immediately reproduce the original analog signal.Further, when an amplitude data value on a sample point at time T3 and atiming data value between the sample points T2 and T3 are inputted, aninterpolating operation is performed therebetween so as to immediatelyreproduce the original analog signal. The same operation is sequentiallyperformed at the following time.

As described above, according to the present embodiment, it is possibleto directly compress and expand an analog signal to be compressed on atime base without time/frequency conversion. Hence, it is also possibleto simplify the configuration without complicated operations. Further,when compressed data is transmitted from the compression side and isreproduced on the expansion side, inputted compressed data can besequentially processed and reproduced by a simple interpolatingoperation on a time base, thereby achieving real-time operations.

Besides, the interpolating operation represented by the above equations(6) and (7) can also be realized by hardware such as a logic circuit andby DSP (Digital Signal Processor) or software (a program stored in ROM,RAM, and the like).

The following will discuss another example of the above datainterpolation. Here is the description of a method of computing aninterpolation value by double oversampling and convolution that useamplitude data values D1 and D2 on successive sample points and a timingdata value T therebetween FIG. 7 is a diagram showing the results ofperforming oversampling and convolution (D1=7, D2=3, T=5) on time of T1and T2 of FIG. 2.

In FIG. 7, a number “4” on the leftmost series r1 indicates a differencevalue (=D1−D2) of two amplitude data values D1 and D2. The ten “4” arearranged in a vertical direction to indicate that a difference value ofthe amplitude datavalues D1 and D2 is stored in D-type flip flops (notshown) making cascade connection while being sequentially delayed by oneclock. The number of the D-type flip flops is twice a timing data valueT=5.

Further, the second numeral series r2 from the left indicates the resultof shifting the sample values of the first column r1 by one clock.Moreover, the third to fifth numeral series r3, r4, and r5 indicate theresults of further shifting the sample values of the second numeralseries r2 sequentially by one clock.

Besides, the sixth numeral series r6 indicates the result of adding thefirst to fifth numeral series r1 to r5 on each corresponding row, thatis, the result of performing five-stage convolution on the first tofifth numeral series r1 to r5. Also, the seventh to tenth numeral seriesr7, r8, r9, and r10 indicate the results of further shifting the samplevalues of the sixth column r6 sequentially by one clock afterconvolution.

Also, the eleventh numeral series r11 indicates the result of adding thesixth to tenth numeral series r6 to r10 on each corresponding row, thatis, the result of performing five-stage convolution on the sixth totenth numeral series r6 to r10. Further, the twelfth numeral series r12indicates the result of further shifting the sample values of theeleventh numeral series r11 by one clock after convolution.

Further, the thirteenth numeral series r13 indicates the result ofadding the eleventh and twelfth numeral series r11 and r12 on eachcorresponding row. When the thirteenth numeral series r13 obtained byaddition is represented by Mt, an interpolation value SOUT forinterpolating two amplitude data values D1 and D2 is expressed by thefollowing equation.

S _(OUT)=D1−M1 (D1−D2)/(8T?T)=7−Mt/50

The interpolation value S_(OUT) is plotted as shown in the graph of FIG.7, and the same analog signal can be reproduced as time T1 and T2 ofFIG. 1.

Incidentally, when two amplitude data values D1 and D2 are reversedbetween a small value and a large value, for example, in the case ofD1=3 and D2=7, double oversampling and convolution are performed asshown in FIG. 8.

The original analog signal of FIG. 1 can be reproduced by performingsuch data interpolation sequentially between all sample points.Additionally, the operations of FIGS. 7 and 8 can be performed byhardware having a plurality of D-type flip flops, adders, andmultipliers that are combined as necessary for storing data values whilemaking one-clock delay.

Next, the following will discuss a configuration for realizing theabove-mentioned compression and expansion. FIG. 9 is a block diagramshowing an example of the configuration of a compression apparatusaccording to the present embodiment.

In FIG. 9, in order to readily detect a sample point, the input analogsignal 101 is converted to digital data by an A/D converter 104 afternoise is removed by an LPF 103. At this moment, the A/D converter 104performs A/D conversion according to a clock CK1 having a doublefrequency (88.2 KHz). The clock CK1 is generated by a PLL (Phase LockedLoop) circuit 105 from an input clock CK0 having a predeterminedfrequency (e.g., 44.1 KHz in the case of an aural signal).

An average value interpolation data generating section 106 performsoversampling with a double frequency on digital data outputted from theA/D converter 104. And then, regarding a plurality of sample valuesobtained thus, average values are computed between successive samplevalues to generate interpolation data. Namely, when inputted digitaldata undergoes oversampling, a numeral series having the same two valuessuccessively is obtained. Regarding such a numeral series, when anaverage value is computed by using the same successive values, thevalues remain the same. When an average value is computed by usingdifferent successive values, an intermediate value is obtained betweenthe different values.

FIG. 10 is a block diagram showing an example of the configuration ofthe average value interpolation data generating section 106. In FIG. 10,a D-type flip flop 201 stores digital data, which is outputted from theA/D converter 104 of FIG. 9, according to a reference input clock CK0.Further, a D-type flip flop 202 connected to the subsequent stage storesdigital data, which is outputted from the D-type flip flop 201,according to a clock CK1 having a frequency twice that of the aboveinput clock CK0.

And then, an adder 203 adds digital data stored in the two D-type flipflops 201 and 202, and outputs the results to a half multiplier 204. Thehalf multiplier 204 divides the addition results of the adder 203 by afactor of 2, and a D-type flip flop 205 stores the results according tothe clock CK1 having a double frequency. Subsequently, the digital datastored in the D-type flip flop 205 is outputted as interpolation datagenerated by double oversampling.

Since such an average value interpolation data generating section 106 isprovided, it is possible to always set a timing data value at an evennumber. The timing data value is indicative of a time interval betweensample points having differential absolute values at a predeterminedvalue or smaller. Thus, it is not necessary to separately performcomplicated operations for an even number and an odd number. Besides, inaddition to oversampling, an average value of successive sample valuesis computed and outputted. Hence, a stepwise data waveform can be formedinto a smooth waveform close to the original analog waveform. Therefore,it is possible to improve reproducibility of the original analog signalwhen expansion is performed by an decompression apparatus, which will bediscussed later.

Digital data undergoing oversampling in the average value interpolationdata generating section 106 is inputted to a timing synthesizer 107 anda compressing section 108. The timing synthesizer 107 differentiatesdigital data supplied from the average value interpolation datagenerating section 106 and detects sample points. And then, the timingsynthesizer 107 computes and outputs a sampling clock indicative oftiming of the detected point and timing data (the number of clocks CK1having a double frequency) indicative of a time interval between thesample points.

FIG. 11 is a block diagram showing an example of the configuration ofthe timing synthesizer 107. In FIG. 11, a differentiator 301differentiates digital data inputted from the average valueinterpolation data generating section 106. Further, a sample pointdetecting section 302 detects sample points, on which digital data hasdifferential absolute values at a predetermined value or smaller, basedon the differentiation results of the differentiator 301.

A timing generating section 303 counts the number of clocks CK1 having adouble frequency. The clocks CK1 are supplied from when a sample pointis detected to when a subsequent sample point is detected. The timinggenerating section 303 outputs the number as timing data and outputs asampling clock indicative of timing of a detected point of each samplepoint. Also, the timing generating section 303 also generates andoutputs a reading clock, which will be discussed later.

Moreover, the compressing section 108 takes out only digital data on thecorresponding sample point and outputs it as amplitude data according toa sampling clock outputted from the timing synthesizer 107. A FIFOmemory 109 captures a pair of amplitude data on each sample point andtiming data indicative of a time interval between sample points,according to a sampling clock. The amplitude data is outputted from thecompressing section 108 and the timing data is outputted from the timingsynthesizer 107. And then, the FIFO memory 109 reads the data in orderaccording to a reading clock. A pair of amplitude data and timing datathat is read therefrom is transmitted or recorded as compressed data.

FIG. 12 is a block diagram showing an example of the configuration ofthe decompression apparatus of the present embodiment. In FIG. 12, aclock generator 401 generates a clock CK1 having a double frequency froma reference input clock CK0. Besides, a timing generator 402 generates areading clock, which is indicative of time intervals as irregular as thesample points detected on the compression side, from the clock CK1having a double frequency in response to timing data included incompressed data.

A D-type flip flop 403 captures and stores in order amplitude data,which is included in compressed data, at timing according to a readingclock generated by the timing generator 402, and the D-type flip flop403 outputs the amplitude data to an expanding section 404. Amplitudedata on an input/output stage of the D-type flip flop 403, that is,amplitude data stored in the D-type flip flop 403 at timing of a readingclock and amplitude data to be stored in the D-type flip flop 403 attiming of a subsequent reading clock (two pieces of amplitude data ontwo successive sample points) are inputted to the expanding section 404.

The expanding section 404 generates digital interpolation data betweensample points by an interpolating operation of the above equations (6)and (7) or convolution shown in FIGS. 7 and 8, by using two pieces ofamplitude data inputted thus and timing data inputted from the timinggenerator 402. And then, after digital interpolation data generated thusis converted to an analog signal by a D/A converter 405, the signal isoutputted as a reproduced analog signal via an LPF 406.

As specifically described above, in the present embodiment, since aninput analog signal varying smoothly is sampled on the compression sideat irregular time intervals having differential absolute values at apredetermined value or smaller, it is possible to obtain discreteamplitude data values and timing data values indicative of irregulartime intervals as compressed data. And then, on the expansion side,according to amplitude data values and timing data values that areincluded in compressed data, discrete data is read at time intervals asirregular as the compression side, and an analog signal is outputted,which connects pieces of the data by interpolation.

Therefore, when an analog signal on a time base is compressed andexpanded, processing can be carried out on a time base without frequencyconversion. For this reason, compression and expansion is notcomplicated and the configuration thereof can be simplified. Further,when compressed data is transmitted from the compression side andreproduced on the expansion side, compressed data to be inputted to theexpansion side can be processed and reproduced in order by a simpleinterpolating operation on a time base, thereby achieving real-timeoperations.

Moreover, in the present embodiment, points where digital data hasdifferential absolute values at a predetermined value or smaller aredetected as sample points, compressed data is generated from amplitudedata values on the detected sample points and timing data valuesindicative of time intervals of the sample points, and the compresseddata is transmitted or recorded. Hence, only data on the sample pointscan be obtained as compressed data, achieving a high compressibility.

Furthermore, according to the present embodiment, inflection points,which exist in a signal to be compressed, are detected as sample points.Thus, compressed data includes all minimum points required forreproducing original data by an interpolating operation on the expansionside. Therefore, it is possible to obtain high-quality reproduced datawith a higher reproducibility of original data.

Additionally, although Embodiment 1 describes that an input signal to becompressed is an analog signal, an input signal may be a digital signal.In this case, the LPF 103 and the A/D converter 104 of FIG. 9 are notnecessary, and the D/A converter 405 and the LPF 406 of FIG. 12 are notnecessary.

Besides, although the average value interpolation data generatingsection 106 performs double oversampling in Embodiment 1, the multipleis not limited to double as long as it is even.

(Embodiment 2)

Hereinafter, Embodiment 2 of the present invention will be discussed inaccordance with the accompanied drawings. Embodiment 2 is devised toinput and compress digital data. In a compression apparatus of thepresent embodiment, n-times oversampling and a moving average operationor a convoluting operation (hereinafter, referred to as convolution) areperformed on inputted digital data to be compressed. Hence, it ispossible to obtain smoother data in which pieces of discrete data areconnected by interpolation.

Subsequently, from a series of data obtained thus, a position having adifferential absolute value smaller than previous and subsequentpositions, that is, a position having a minimum differential absolutevalue is detected as a sample point. And then, an amplitude data valueon each detected sample point and a timing data value indicative of atime interval of the sample points are obtained, and a pair of theamplitude data value and the timing data value is transmitted orrecorded as compressed data.

FIG. 13 is a block diagram showing an example of the entireconfiguration of a compression apparatus for realizing the abovecompression method according to the present embodiment.

As shown in FIG. 13, the compression apparatus of the present embodimentis constituted by an oversampling circuit 1, a PLL (Phase Locked Loop)circuit 2, a differentiator 3, a compressed data generating section 4,an error correction coding section 5, and a data memory 6.

The oversampling circuit 1 performs n-times oversampling and convolutionon inputted digital data to be compressed so as to compute a digitalinterpolation value for connecting pieces of discrete data. In theexample of FIG. 13, as data to be compressed, the oversampling circuit 1inputs voice data sampled at a frequency of 44.1 KHz, performsoversampling on the data at an eight-times frequency (352.8 KHz), andperforms convolution. And then, the oversampling circuit 1 outputs aseries of oversampled data obtained thus to the differentiator 3 and thecompressed data generating section 4.

The PLL circuit 2 generates a clock 8CLK having an eight-times frequency(352.8 KHz) from an input clock CLK having a reference frequency (44.1KHz) and supplies the clock 8CLK to the compressed data generatingsection 4, the error correction coding section 5, and the data memory 6as well as the above oversampling circuit 1. The oversampling circuit 1,the compressed data generating section 4, the error correction codingsection 5, and the data memory 6 operate in synchronization with theclock 8CLK having an eight-times frequency.

The differentiator 3 differentiates a series of oversampled datagenerated in the oversampling circuit 1 on each sampling point, andcomputes an absolute value thereof and outputs it to the compressed datagenerating section 4.

The compressed data generating section 4 detects as a sample point aposition having a differential absolute value smaller than previous andsubsequent positions, from a series of oversampled data supplied fromthe oversampling circuit 1. And then, a pair of an amplitude data valueon each detected sample point and a timing data value indicative of atime interval of sample points is outputted to the error correctioncoding section 5. The compressed data generating section 4 also obtainsa timing clock indicative of timing of a detected point on each samplepoint and outputs it to the data memory 6.

The error correction coding section 5 adds an error correcting code todata supplied from the compressed data generating section 4 in order todetect and accurately correct a varied bit even when digital data on atransmission line or a memory is changed by noise and the like and anerror occurs. And then, the data obtained thus is outputted to atransmission line or the data memory 6 as compressed data.

The data memory 6 is a record medium for storing compressed data. Thedata memory 6 records compressed data, which is generated by the errorcorrection coding section 5, according to a timing clock from thecompressed data generating section 4. Further, the data memory 6 readsand outputs stored compressed data in response to a reading requestsignal REQ supplied from outside.

FIG. 14 is a block diagram showing an example of the entireconfiguration of an decompression apparatus for realizing andecompression method corresponding to the above compression methodaccording to the present embodiment.

As shown in FIG. 14, the decompression apparatus of the presentembodiment is constituted by an error correcting circuit 11, a clockgenerator 12, a timing generator 13, a D-type flip flop 14, an expandingsection 15, a D/A converter 16, and a low-pass filter (LPF) 17.

The error correcting circuit 11 inputs compressed data generated in thecompression apparatus of FIG. 13, detects a bit varied on a transmissionline or memory, and corrects an error, by using an error correcting codeadded to the data.

The clock generator 12 generates a clock 8CLK having an eight-timesfrequency from an input clock CLK having a reference frequency andsupplies the clock 8CLK to the timing generator 13, the expandingsection 15, and the D/A converter 16. Also, the timing-generator 13receives from the error correcting circuit 11 timing data included incompressed data, generates a reading clock, which is indicative of timeintervals as irregular as sample points detected on the compressionside, from the clock 8CLK having an eight-times frequency, and suppliesthe reading clock to the error correcting circuit 11 and the D-type flipflop 14.

The D-type flip flop 14 sequentially captures and stores amplitude data,which is included in compressed data, from the error correcting section11 at timing corresponding to a reading clock generated by the timinggenerator 13, and the D-type flip flop 14 outputs the amplitude data tothe expanding section 15. Amplitude data of an input/output stage of theD-type flip flop 14, that is, amplitude data stored in the D-type flipflop 14 at timing of a reading clock and amplitude data to be stored inthe D-type flip flop 14 at timing of the subsequent reading clock (twopieces of amplitude data on two successive sample points) are inputtedto the expanding section 15.

The expanding section 15 generates digital interpolation data betweenthe sample points by an interpolating operation and so on, which will bediscussed later, using two pieces of amplitude data inputted thus andtiming data inputted by the timing generator 13. The D/A converter 16converts digital interpolation data generated thus to an analog signal.Further, the LPF 17 performs a low-pass filter operation on an analogsignal outputted from the D/A converter 16 so as to remove noise, andthe analog signal is outputted as a reproduced analog signal.

Next, the following will discuss the details of the configuration andoperations of the oversampling circuit 1 in the compression apparatus ofFIG. 13.

Here, before describing the oversampling method of the presentembodiment for computing an interpolation value between pieces ofdiscrete digital data, a typical interpolating method conventionallyused will be firstly discussed.

Data interpolation, which interpolates pieces of discrete digital datato obtain more continuous pieces of data, is carried out as shown inFIG. 5 by using, for example, a sampling function referred to as a sincfunction of FIG. 4. The sinc function is defined as sin (?ft)/(?ft) whena sampling frequency is f. A value is set at 1 only on a sampling pointof t=0, and values are all set at 0 on all of the other sampling points(t=1, ±2, ±3, ±4, . . . ) disposed at regular intervals.

Unlike a typical data interpolating method using such a sinc function,in the oversampling circuit 1 of the present embodiment, when aninterpolation value is computed between two pieces of discrete data,each piece of digital data of a basic waveform undergoes oversampling.The waveform has amplitudes corresponding to n pieces of discrete datavalues that include the two pieces of discrete data. Further, theobtained n pieces of data are synthesized by convolution so as todigitally compute an interpolation value for connecting the two piecesof discrete data.

FIG. 15 is an explanatory drawing showing a digital basic waveform usedin the present embodiment. The digital basic waveform of FIG. 15 is abasic sampling function, which is used when data is interpolated by oversampling. The digital basic waveform is formed by changing a data valueto −1, 1, 8, 8, 1, and −1 for each clock (CLK) having a referencefrequency.

Referring to FIG. 16, the following will discuss a principle of datainterpolation according to the present embodiment, by taking as anexample the case where an interpolation value is generated by n-timesoversampling and convolution from discrete data values (−1, 1, 8, 8, 1,−1)/8, which correspond to a normalized digital basic waveform shown inFIG. 15. Besides, in consideration of a space of the drawing, FIG. 16shows an example of four-times oversampling. The oversampling circuit 1of FIG. 13 actually performs eight-times oversampling.

In FIG. 16, a numeral series shown on the leftmost side indicates valuesobtained by performing four-times oversampling on original discrete datavalues of (−1, 1, 8, 8, 1, −1)/8. Further, in four numeral series fromthe leftmost side to the right, the values on the leftmost side areshifted downward one by one. A direction of the numeral seriesrepresents a time base in FIG. 16. Shifting a numeral series downward isequivalent to gradual delay of the numeral series indicated on theleftmost side.

Namely, the second numeral series from the left indicates a numeralseries shifted from the leftmost numeral series by a quarter phase of aclock 4CLK having a quadruple frequency. Moreover, the third numeralseries from the left indicates a numeral series shifted from the secondnumeral series from the left by a quarter phase of the clock 4CLK havinga quadruple frequency. The fourth numeral series from the left indicatesa numeral series shifted from the third numeral series from the left bya quarter phase of the clock 4CLK having a quadruple frequency.

Further, the fifth numeral series from the left has values obtained byadding values of the first to fourth numeral series on each of thecorresponding rows and dividing the added values by four. The operationson the first to fifth numeral series from the left can digitally performquadruple oversampling together with four-phase convolution.

Four numeral series from the fifth numeral series to the right (fifth toeighth numeral series from the left) indicate numeral series shifteddownward one by one from the fifth numeral series. Also, the ninthnumeral series from the left has values obtained by adding values of thefifth to eighth numeral series on each of the corresponding rows anddividing the added values by four. The operations on the first to ninthnumeral series from the left can digitally perform quadrupleoversampling twice together with four-phase convolution.

Further, the tenth numeral series from the left is a numeral seriesshifted downward by one from the ninth numeral series. Besides, theeleventh numeral series (on the rightmost side) from the left has valuesobtained by adding values of the ninth and tenth numeral series on eachof the corresponding rows and dividing the added values by two. Thevalues on the rightmost side are target interpolation values.

FIG. 17 is a graph showing the finally obtained numeral series on therightmost side of FIG. 16. A function having a waveform of FIG. 17 canbe differentiated for one time throughout a range. The function has alimited value other than 0 when a sampling position t along a lateralaxis is 1 to 33, and the function has values all set at 0 in otherregions.

When the function has a limited value other than 0 on a local region andhas 0 in other regions, the state is referred to as a “definite base”.

Also, the function of FIG. 17 is a sampling function characterized byhaving a maximum value only on a sample point of t=17 and a value of 0on four sample points of t=1, 9, 25, 33. The function passes through allsample points required for obtaining data with a smooth waveform.

As described above, the function of FIG. 17 is a sampling function anddifferentiation is possible for one time throughout the region.Additionally, the function has a definite base, which converges to 0 atsampling positions of t=1, 33. Therefore, since superposition is made byusing the sampling function of FIG. 17 based on each piece of discretedata, it is possible to interpolate a value between pieces of discretedata by using the function, which can be differentiated for one time.

The conventionally used sinc function converges to 0 on a sample pointof t=±?. Thus, when an interpolation value is computed accurately, it isnecessary to calculate a value of the sinc function on an interpolatingposition for each piece of discrete data until t=±? and to perform aconvoluting operation using the value. In contrast, the samplingfunction of FIG. 17 used in the present embodiment converges to 0 onsample points of t=1, 33. Hence, only discrete data within a range oft=1 to 33 needs to be considered.

Therefore, when a certain interpolation value is obtained, only valuesof limited n pieces of discrete data need to be considered, therebylargely reducing an amount of processing. Additionally, discrete databeyond the range of t=1 to 33 is ignored. This is not because aprocessing quantity, accuracy, and so on need to be considered butbecause the discrete data does not need to be considered theoretically.Thus, a censoring error does not occur. Therefore, it is possible toaccurately obtain an interpolation value by using the data interpolationof the present embodiment and to improve the reproducibility of originaldata before compression regarding data reproduced on the expansion sidewhen compression is performed using the accurate interpolation value.

FIG. 18 is a block diagram showing an example of the configuration ofthe oversampling circuit 1 shown in FIG. 13. As shown in FIG. 18, theoversampling circuit 1 of the present embodiment is constituted by anormalized data memory 21, a phase shifting section 22, a plurality ofdigital multipliers 23 a to 23 d, and a plurality of digital adders 24 ato 24 c. Besides, a PLL circuit 2 of FIG. 18 is identical to that ofFIG. 13.

The normalized data memory 21 shifts a series of normalized data in fourphases and stores the data as shown on the rightmost side of FIG. 16.Additionally, FIG. 16 shows an example in which quadruple oversamplingis performed on the digital basic waveform of FIG. 15. Since theoversampling circuit 1 of FIG. 13 performs eight-times oversampling, inthe normalized data memory 21, a digital basic waveform undergoeseight-times oversampling and a series of data normalized by convolutionis stored therein. Four-phase normalized data stored in the normalizeddata memory 21 is read in response, to clocks CLK and 8CLK supplied fromthe PLL circuit 2, and the data is supplied to one of the inputterminals of each of the four digital multipliers 23 a to 23 d.

Moreover, the phase shifting section 22 performs a phase shiftingoperation for shifting the phase of discrete data, which is inputted asdata to be compressed, to four phases. Four-phase discrete datagenerated by the phase shifting section 22 is outputted in response tothe clocks CLK and 8CLK supplied from the PLL circuit 2, and the data issupplied to the other input terminal of each of the four digitalmultipliers 23 a to 23 d.

The four digital multipliers 23 a to 23 d multiply four-phase normalizeddata, which is outputted from the normalized data memory 21, andfour-phase discrete data, which is outputted from the phase shiftingsection 22. The three digital adders 24 a to 24 c, which are connectedto the subsequent stage of the multipliers, add all the multiplicationresults of the four digital multipliers 23 a to 23 d and output theresults of the addition to the differentiator 3 and the compressed datagenerating section 4 of FIG. 13.

In the configuration of the oversampling circuit 1 shown in FIG. 18, thenormalized data memory 21 constitutes storing means of the presentinvention. Further, the phase shifting section 22, the digitalmultipliers 23 a to 23 d, and the digital adders 24 a to 24 c constitutesynthesizing means of the present invention.

As shown in the configuration of FIG. 18, in the present embodiment, thenormalized data memory 21 such as ROM stores in advance normalized data,which is obtained by convolution on the rightmost side of FIG. 16. Andthen, the normalized data is modulated to amplitude corresponding to avalue of discrete data inputted as data to be compressed. The obtaineddata is synthesized by four-phase convolution and is outputted.

An amplitude value of discrete data, which is inputted as data to becompressed, may be multiplied relative to the digital basic waveform ofFIG. 15, and convolution of FIG. 16 may be performed on an obtained datavalue during compression. In the case of the oversampling circuit 1configured as FIG. 18, it is not necessary to perform convolution ofFIG. 16 during actual compression, thereby increasing a compressionspeed.

FIG. 19 is a diagram showing an example of digital data inputted to theoversampling circuit 1. FIG. 20 is a diagram showing output data afterthe oversampling circuit 1 performs data interpolation on the digitaldata. As shown in the above diagram, with the oversampling circuit 1 ofthe present embodiment, it is possible to obtain continuous oversampleddata, in which values change more smoothly, from original discretedigital data.

Next, as for digital data undergoing such oversampling, the followingwill discuss in detail the operation of generating compressed data byusing the differentiator 3 and the compressed data generating section 4of FIG. 13, and the operation of decompression compressed data by usingthe timing generator 13, the D-type flip flop 14, and the expandingsection 15 of FIG. 14.

First, the compression operation will be discussed. As described above,the differentiator 3 of FIG. 13 differentiates a series of oversampleddata, which is generated in the oversampling circuit 1, on each samplingpoint, and obtains an absolute value of the data and outputs it to thecompressed data generating section 4.

FIG. 21 is a diagram showing an example of the configuration of thedifferentiator 3. As shown in FIG. 21, the differentiator 3 of thepresent embodiment is composed of a difference absolute value circuitfor computing a difference absolute value between pieces of data on twosuccessive sampling points.

In FIG. 21, subtracters 31 and 32 respectively compute differencesbetween pieces of data on two successive sampling points, the data beinginputted from nodes a and b. Namely, the subtracter 31 computes adifference a−b, and the subtracter 32 computes a difference b−a. Theresults are respectively outputted to OR circuits 33 and 34. Thesubtracters 31 and 32 output a value of “1” as a bollow in addition todifference values when computed difference values are negative.

The OR circuit 33 ORs a difference value and bollow output that arecomputed in the subtracter 31, and outputs the results to an AND circuit35. Moreover, the other OR circuit 34 ORs a difference value and bollowoutput that are computed in the subtracter 32, and outputs the resultsto the AND circuit 35. The AND circuit 35 ANDs the outputs from the twoOR circuits 33 and 34 and outputs the results to a node c. Also, thebollow output of the subtracter 31 is outputted to a node d, and adifference value computed in the subtracter 32 is outputted to a node e.

Therefore, a difference absolute value |a−b| of data on two successivesampling points is outputted to the node c, a value of “1” is outputtedto the node d when a data value of the node b is larger than that of thenode a, and a difference value b−a between pieces of data of the nodes aand b is outputted to the node e.

Besides, for explanation, FIG. 21 shows only one-bit data lines of thenodes a, b, c, and e. Actually, data lines are equivalent to the numberof bits.

The compressed data generating section 4 of FIG. 13 detects as a samplepoint a point where a differential absolute value is smaller than thoseof previous and subsequent positions, from a series of oversampled datasupplied from the oversampling circuit 1. And then, a pair of anamplitude data value on each detected sample point and a timing datavalue indicative of a time interval of sample points is outputted to theerror correction coding section 5.

In the present embodiment, when a sample point is detected based on adifferential absolute value computed in the differentiator 3, in orderto provide a margin for determining a sample point, determination ismade after dropping a lower-order bit of a difference absolute valuecomputed by the differentiator 3. For example, when one bit of a lowerorder is dropped, determination can be made on the assumption that adifference absolute value is always 0 when an actually computeddifference absolute value ranges from 0 to 1. Also, when two bits of alower order are dropped, determination can be made on the assumptionthat a difference absolute value is always 0 when an actually computeddifference absolute value ranges from 0 to 3. With this operation, it ispossible to avoid influence of slight change such as noise, andunnecessary points are not detected as sample points, thereby increasingcompressibility.

FIG. 22 is a diagram showing the results of computing a differentialabsolute value by the differentiator 3 regarding data outputted from theoversampling circuit 1 of FIG. 20. As described above, the compresseddata generating section 4 detects a point where a differential absolutevalue is smaller than those of previous and subsequent points, that is,a point where a minimum differential absolute value appears (positionindicated by arrows of FIG. 22) as a sample point, based on output dataof a differential absolute value shown in FIG. 22. Besides, minimumvalues appearing on the first and last point may be incorrect datavalues. Thus, such a point is not adopted as a sample point.

When a lower-order bit of a differential absolute value is dropped toprovide a margin for detecting a sample point, two equal minimum valuesmay appear successively. In this case, the polarity of a differentialvalue is determined based on a bollow value of the subtracter 31, thebollow value being outputted to the node d of the differentiator 3 shownin FIG. 21, and a point where a differential value changes in polarityis detected as a sample point.

Furthermore, when a differential value does not change in polarity, asshown in FIG. 23, in view of the relationship between differentialabsolute values on sampling points A and D disposed before and after twosuccessive sampling points B and C having equal values, a point closerto a smaller value is detected as a sample point. In the example of FIG.23, since the sampling point D is smaller than the sampling point A indifferential absolute value, the sampling point C closer to the samplingpoint D is detected as a sample point.

As an operation for detecting a sample point, double differentiation isperformed as follows: after data supplied from the oversampling circuit1 is differentiated once, an obtained differential absolute value isfurther differentiated. A point just before a double differential valuechanges in polarity from negative or 0 to positive may be extracted as asample point. Further, from points extracted thus based on the polarityof double differential values, only a point where a first differentialabsolute value is smaller than a fixed value may be detected as a normalsample point.

In other words, on a minimum point of a differential absolute valueobtained by first differentiation, a double differential value, which isobtained by further differentiating a first differential absolute value,surely changes in polarity from negative to positive. Thus, when adouble differential value of oversampled data is computed and a pointwhere polarity changes from negative to positive (including a pointhaving a double differential value of 0) is detected, a minimum point ofa first differential absolute value can be detected accurately.Furthermore, even when two successive minimum points appear with equalvalues, one of them can be positively detected as a sample point.Moreover, by detecting as a normal sample point only a point where afirst differential absolute value is below a fixed value, it is possibleto prevent an unnecessary point from being detected as a sample point,thereby increasing compressibility.

FIG. 24 is a block diagram showing an example of the configuration fordetecting a sample point by performing the above double differentiation.FIG. 24 shows examples of the configurations of the differentiator 3 andthe compressed data generating section 4 that are shown in FIG. 13.

As shown in FIG. 24, the differentiator 3 is provided with a firstdifferentiating section 41, a rounding section 42, and a seconddifferentiating section 43. Additionally, the compressed data generatingsection 4 is provided with a polarity changing point detecting section44, a threshold value processing section 45, and a data generatingsection 46.

The first differentiating section 41 differentiates oversampled datasupplied from the oversampling circuit 1 of FIG. 13 for each samplingpoint and computes and outputs an absolute value of the data. Therounding section 42 drops a lower-order bit of a first differentialabsolute value computed by the first differentiating section 41. Forexample, three bits of a lower order are dropped by dividing the abovefirst differential absolute value by eight, thereby removing theinfluence of slight change caused by noise. Data outputted from therounding section 42 is supplied to the second differentiating section 43and the threshold value processing section 45 in the compressed datagenerating section 4.

The second differentiating section 43 further differentiates a firstdifferential absolute value, which is rounded by the rounding section42, for each sampling point. A double differential value computed by thesecond differentiating section 43 and a bollow value indicative of itspolarity are supplied to the polarity changing point detecting section44 in the compressed data generating section 4.

As a candidate of a sample point, the polarity changing point detectingsection 44 extracts a point just before a double differential valuesupplied from the second differentiating section 43 in thedifferentiator 3 changes in polarity from negative to positive, forexample, the last negative point when double differential values withnegative polarity are successively obtained, or a point where a doubledifferential value is 0. When double differential values are notsuccessively obtained with negative polarity, the corresponding negativepoint may be further extracted as a candidate of a sample point.

The threshold value processing section 45 compares a first differentialabsolute value supplied from the rounding section 42 and a predeterminedthreshold value, regarding candidates of sample points that areextracted from the polarity changing point detecting section 44. Thethreshold value processing section 45 detects as a normal sample pointonly a point where a first differential absolute value is smaller than athreshold value and transmits the point to the data generating section46.

The data generating section 46 obtains an amplitude data value on eachsample point detected thus, from oversampled data supplied from theoversampling circuit 1. The data generating section 46 generates atiming data value indicative of a time interval of sample points byusing a clock 8CLK, which is supplied from the PLL circuit 2 with aneight-times frequency. And then, a pair of the amplitude data value andthe timing data value is outputted as compressed data.

Additionally, in the example of FIG. 24, a threshold value is processedusing a first differential absolute value rounded by the roundingsection 42. A threshold value may be processed using a firstdifferential absolute value computed by the first differentiatingsection 41 before rounding. Further, in FIG. 24, a point just before adouble differential value changes in polarity from negative to positiveis extracted as a sample point. A point just after polarity changes fromnegative to positive may be extracted as a sample point. Moreover, theprocessing of a threshold value of FIG. 24 is not limited to doubledifferentiation for detecting a sample point. The processing isapplicable when a sample point is detected by one-time differentiation.

FIG. 25 is a diagram showing compressed data (pair of an amplitude datavalue and a timing data value on each sample point) outputted accordingto the example of FIG. 22. For example, determination data (two bits),which determines a signal type, and an error correcting code are addedto compressed data outputted thus. Thereafter, compression such asvariable-length coding may be further carried out.

The principles of compression and expansion of Embodiment 2 are alsoshown in FIGS. 1 and 2. However, in the case of the present embodiment,the waveform data of FIG. 1 corresponds to oversampled data, which isgenerated continuously by data interpolation of the oversampling circuit1. Moreover, the waveform data of FIG. 2 corresponds to data obtained bythe process for reproducing original oversampled data by expansion.

Referring to FIG. 1, compression will be firstly discussed. In thepresent embodiment, from inputted oversampled data 101, sample points102 a to 102 f having minimum differential absolute values are detected.And then, amplitude digital data values on the sample points 102 a to102 f and timing data values indicative of time intervals of the samplepoints 102 a to 102 f are obtained. A pair of an amplitude data valueand a timing data value is outputted to the error correction codingsection 5 of FIG. 13 as compressed data.

Referring to FIG. 2, the following will discuss an decompressionoperation of data compressed as shown in FIG. 1. When input data 101 iscompressed according to the compression method of FIG. 1, obtainedcompressed data is a numeral series of (*, 7), (5,3), (7,9), (3,1),(3,6), and (3,3). Here, * indicates that no value is shown in FIG. 1.Further, compressed data is inputted in the above order to the timinggenerator 13 and the D-type flip flop 14 on the expansion side.

First, in the expanding section 15 of FIG. 14, data of a waveform a1 isgenerated by an interpolating operation from two data values of anamplitude data value “7” and a timing data value “5”, which are firstlyoutputted from the error correction coding section 11. Next, data of awaveform a2 is generated by an interpolating operation from two datavalues of the above timing data value “5” and an amplitude data value“3”, which is subsequently inputted.

Subsequently, data of a waveform b2 is generated by an interpolatingoperation from two data values of the above amplitude data value “3” anda timing data value “7”, which is subsequently inputted. Further, dataof a waveform b1 is generated by an interpolating operation from theabove timing data value “7” and an amplitude data value “9”, which issubsequently inputted. In this manner, data of waveforms c1, c2, d2, d1,e1, and e2 is generated in order by using combinations of successivelyinputted amplitude data values and timing data values.

The above operation generates digital data (upper stage of FIG. 2)having continuous waveforms a1, b1, c1, d1, and e1, and digital data(lower stage of FIG. 2) having continuous waveforms a2, b2, c2, d2, ande2. And then, the expanding section 15 adds the two pieces of digitaldata generated thus, outputs the data to the D/A converter 16, andperforms digital-analog conversion thereon. Thus, an analog signal isreproduced, which corresponds to the oversampled data 101 of FIG. 1.

As data interpolation performed by synthesizing digital data on theupper stage and digital data on the lower stage of FIG. 2, for example,the operation described in FIG. 6 is applicable.

Besides, in Embodiment 2, since eight-times oversampling is carried outduring compression, a timing data value indicative of a time intervalbetween sample points is not an odd number but is always an even number(corresponding to 2T on a lateral axis of FIG. 6). Namely, the fivetiming data values “5, 7, 3, 3, 3” shown in FIG. 1 are actuallytransmitted or stored as values of “40, 56, 24, 24, 24” by eight-timesoversampling.

When a timing data value T is an odd number, an interpolating position tis not placed just on an intermediate point between sample points. Thus,the operations need to be performed separately for an even number and anodd number of timing data values. However, in the case of the presentembodiment, a timing data value indicative of a time interval betweensample points is always an even number. Hence, it is not necessary toperform complicated operations such as separate operations for an evennumber and an odd number.

Next, another example of the above data interpolation will be discussedbelow. Here, the following will describe a method of determining aninterpolation value by double oversampling and convolution usingamplitude data values D1 and D2 on successive sample points and a timingdata value T there between.

FIGS. 26A and 26B are diagrams showing the results of oversampling andconvolution performed on the first two sample points of compressed datashown in FIG. 25 (D1=29.5, D2=24.4, and T=6).

In FIG. 26A, numeric values “29.5” on the leftmost side are values ofthe first amplitude data D1. Twelve numeric values of “29.5” and “0”arranged vertically show that the amplitude data value D1 is stored inD-type flip flops and the like (not shown) making cascade connectionwhile the amplitude data value D1 is delayed in order by one clock. Thenumber of the D-type flip flops is twice as large as T=6, which is atiming data value. Further, the second to sixth numeral series from theleft show the results of shifting the first numeral series in order byone clock.

Moreover, the seventh numeral series shows the result of adding anddividing by six the first to sixth numeral series on each correspondingrow, that is, the result of performing six-phase convolution on thefirst to sixth numeral series. Additionally, the eighth to twelfthnumeral series show the results of further shifting the values, whichare subjected to convolution on the seventh numeral series, in order byone clock.

Also, the thirteenth numeral series shows the results of adding anddividing by six the seventh to twelfth numeral series on eachcorresponding row, that is, the results of performing six-phaseconvolution on the seventh to twelfth numeral series. The thirteenthnumeral series on the rightmost side forms a desired interpolation curve(the sampling function a1 in the example of FIG. 2).

In the same manner as FIG. 26A, a sampling function a2 in the samesection as the sampling function a1 is computed by using the same timingdata value T (=6) and another amplitude data value D2 (=24.4). And then,by determining the sum of the computing results, as shown in FIG. 26B,it is possible to obtain an interpolation curve finally determined inthe section. Original oversampled data is reproduced by performing suchdata interpolation sequentially on all of the sample points. Here, theoperation of FIG. 26A can be realized by a hardware structure, whichcombines as necessary a plurality of D-type flip flops, adders, andmultipliers. The D-type flip flops store data values while delaying thedata values by one clock.

Additionally, as another example of data interpolation, the method shownin FIG. 7 is also applicable.

FIG. 27 is a diagram showing oversampled data, which is reproduced fromthe compressed data of FIG. 25.

As shown in comparison between the oversampled data of FIG. 27 that isobtained by expansion and the original oversampled data of FIG. 20 thatis obtained before compression, the expansion of the present embodimentcan reproduce data substantially equal to the original oversampled data.

In the decompression apparatus of FIG. 14, oversampled data reproducedthus is inputted to the D/A converter 16 and undergoes digital-analogconversion. Digital data before D/A conversion has already been acontinuous and smooth signal as shown in FIG. 27. Therefore, unlike aconventional D/A converter, it is not necessary to artificially increasea sampling frequency by using a digital filter. The quality of anoutputted analog signal can be remarkably improved simply by D/Aconversion.

As specifically described above, in Embodiment 2, on the compressionside, oversampling and convolution are performed on inputted discretedigital data to generate continuous data making smooth change, andobtained oversampled data is sampled at irregular time intervals havingminimum differential absolute values. Thus, a discrete amplitude datavalue and a timing data value indicative of irregular time intervals areobtained as compressed data. And then, on the expansion side, accordingto an amplitude data value and a timing data value that are included incompressed data, discrete data is read at a time interval as irregularas the compression side, and continuous pieces of data are outputted.The pieces of data are connected by interpolation.

Therefore, when an analog signal on a time base is compressed andexpanded, the operations can be performed on a time base withoutfrequency conversion. For this reason, the compression and decompressionoperations are not complicated and the configuration for the operationscan be simplified. Moreover, when compressed data is transmitted fromthe compression side and is reproduced on the expansion side, a simpleinterpolating operation on a time base can sequentially process andreproduce compressed data that is inputted on the expansion side. Hence,real-time operations can be realized.

Further, in the present embodiment, a point where digital data has aminimum differential absolute value is detected as a sample point,compressed data is generated from an amplitude data value on eachdetected sample point and a timing data value indicative of a timeinterval of sample points, and the compressed data is transmitted orrecorded. Thus, only data on sample points is obtained as compresseddata, thereby achieving high compressibility.

Furthermore, according to the present embodiment, an inflection pointexisting in a signal to be compressed is detected as a sample point, andcompressed data includes all minimum points required for reproducingoriginal data by an interpolating operation on the expansion side.Therefore, it is possible to improve reproducibility of original data,thereby obtaining high-quality reproduced data.

Additionally, in the present embodiment, when oversampling andconvolution are performed on digital data, a function generated from adigital basic waveform is a sampling function with a definite base thathas a value converging to 0 on a limited sampling position, and thefunction can be differentiated for one time. Thus, when a certaininterpolation value is obtained, only values of a limited number ofpieces of discrete data need to be considered, thereby largely reducingan amount of processing. Besides, since a censoring error does notoccur, an interpolation value can be obtained accurately, and as fordata reproduced on the expansion side when compression is made using theinterpolation value, it is possible to improve reproducibility oforiginal data before compression.

Besides, the convolution discussed in Embodiment 2 is just an exampleand the present invention is not limited to the above convolution.

Moreover, in Embodiment 2, although a digital basic waveform has −1, 1,8, 8, 1, −1, a digital basic waveform is not limited to the aboveexample. Namely, any waveform is applicable as long as an obtainedinterpolating function is differentiated for one time throughout a rangeand has a definite function converging to 0 on a limited samplingposition. For example, the weight on both sides may be 1 or 0 instead of−1. Also, the weight at the center may be set at a value other thaneight. In either case, satisfactory curve interpolation can be achieved.

Furthermore, as an interpolating operation performed in the expandingsection 15 of FIG. 14, the convolution of FIG. 16 may be performed basedon the digital basic waveform of FIG. 15. In this case, successiveinterpolation values can be obtained simply by digital processingreferred to as convolution. Thus, D/A conversion results in a smoothanalog signal. Therefore, it is possible to omit the LPF 17 and tosuppress degradation in phase characteristics that is caused by afilter.

(Embodiment 3)

Hereinafter, Embodiment 3 of the present invention will be discussed inaccordance with the accompanied drawings.

The above Embodiments 1 and 2 adopt an interpolating method of avariable clock length that uses a table in processing on a time base. Incontrast, the following Embodiment 3 can perform compression andexpansion more readily without using a table.

In Embodiment 3, first, when an analog signal is inputted as a signal tobe compressed, the inputted analog signal is subjected to A/D conversionand is converted to digital data. And then, the digital data undergoingA/D conversion is rounded by using a first value and a second value. Afirst value may be equal to a second value, but it is more preferablethat a second value is larger than a first value.

Further, digital data rounded by the first value is differentiated onceon each sampling point, and a point where a differential value changesin polarity is detected as a sample point. Digital data rounded by thesecond value is obtained as compressed amplitude data of each detectedsample point, and timing data indicative of a time interval of samplepoints is obtained. Further, difference data is obtained as for obtainedpieces of the compressed amplitude data, and a pair of the compressedamplitude difference data and timing data is transmitted or recorded ascompressed data.

Meanwhile, on an expansion side of compressed data generated thus,compressed amplitude difference data out of compressed data (pair ofcompressed amplitude difference data and timing data) is oversampledaccording to a clock having a frequency of even-numbered times. Andthen, regarding the compressed amplitude difference data that has beensubjected to oversampling, a code is reversed at an intermediateposition of each section of sample points, the section being indicatedby timing data. As for a data string obtained thus, multiple integral isperformed on each section of the sample points, and then, a movingaverage operation or a convoluting operation (convolution) is carriedout.

Therefore, it is possible to obtain compressed amplitude data having asmooth waveform, which is divided for the sections of the sample points.Next, the compressed amplitude data obtained thus and the above timingdata are used to perform an interpolating operation includingmultiplication performed by the number of bits rounded by the secondvalue on the compression side. Thus, interpolation data is generated,which smoothly connects pieces of amplitude data of the sections.Further, generated interpolation data is subjected to D/A conversion asnecessary to be converted to an analog signal, and the interpolationdata is outputted.

FIG. 28 is a block diagram showing an example of the entireconfiguration of a compression apparatus according to Embodiment 3 forrealizing the above compression method.

FIG. 28 shows the case where digital data sampled at a samplingfrequency such as 44.1 KHz (reference frequency) is inputted as data tobe compressed. The inputted digital data is, for example, signed digitaldata of 16 bits. Hereinafter, compression of an aural signal will bediscussed as an example of digital data.

Besides, although digital data is directly inputted as data to becompressed, an analog signal may be inputted. In this case, an inputstage of the compression apparatus is provided with, for example, an LPFand an A/D converter. Namely, in order to readily detect a sample point,an input analog signal is converted to digital data by the A/D converterafter noise is removed by the LPF.

As shown in FIG. 28, the compression apparatus of the present embodimentis constituted by a timing generator 111, an amplitude generator 112, arounding section 113, a difference computing section 114, an encoder115, and a data memory 116 (option).

The timing generator 111 differentiates inputted digital data for onetime on each sampling point, and detects a sample point in response tochange in polarity of a differential value. And then, timing pulse TPindicative of timing of the detected point and timing data (the numberof clocks CK having a reference frequency) indicative of a time intervalbetween sample points are obtained and outputted. Further, the timinggenerator 111 also generates and outputs various clocks including areading clock of the data memory 116.

Moreover, the amplitude generator 112 takes out only digital data on asample point, which corresponds to timing indicated by timing pulse TPoutputted from the timing generator 111, from digital data on eachsampling point that is sampled and inputted according to a clock CKhaving a reference frequency, and the amplitude generator 112 outputsthe digital data as amplitude data of each sample point.

FIG. 29 is a diagram for explaining the operating principles of thetiming generator 111 and the amplitude generator 112. Here, datainputted to the timing generator 111 and the amplitude generator 112 isdigital data. In FIG. 29, a waveform of digital data is shown in ananalog manner for explanation.

In the present embodiment, from digital data 501 inputted forcompression, points 502 a to 502 f, on which differential values changein polarity and differential values are 0, are detected as samplepoints. And then, amplitude data values on the sample points 502 a to502 f and timing data values indicative of time intervals of the samplepoints 502 a to 502 f are obtained and outputted to the subsequentstage.

In the example of FIG. 29, “D0, D1, D2, D3, D4, and D5” are obtained asdigital amplitude data values on the sample points 502 a to 502 f, and“T1, T2, T3, T4, and T5” are obtained as timing data indicative of timeintervals between time t0 and t1, time t1 and t2, time t2 and t3, timet3 and t4, and time t4 and t5, of the sample points 502 a to 502 f.

At time t0, an amplitude data value “D0” on the sample point 502 a isobtained and a timing data value (not shown), which is indicative of atime interval from when a previous sample point (not shown) is detected,is obtained. Thus, a pair of the data values is outputted as data oftime t0.

Subsequently, at time t1 when the sample point 502 b is detected, atiming data value “T1” is obtained, which is indicative of a timeinterval from time t0 when the sample point 502 a is previouslydetected, and an amplitude data value “D1” on the sample point 502 b isobtained. Thus, a pair of the data values (T1, D1) is outputted as dataof time t1.

Further, at time t2 when the sample point 502 c is detected, a timingdata value “T2” is obtained, which is indicative of a time interval fromtime t1 when the sample point 502 b is previously detected, and anamplitude data value “D2” on the sample point 502 c is obtained. Thus, apair of the data values (T2, D2) is outputted as data of time t2.

In this manner, pairs of (T3, D3), (T4, D4), and (T5, D5) arerespectively outputted as data of time t3, t4, and t5. The data includetiming data values indicative of time intervals between time t2 and t3,t3 and t4, and t4 and t5, and amplitude data values detected at time t3,t4, and t5 on the sample points 502 d, 502 e, and 502 f.

FIG. 30 is a block diagram showing an example of the configuration ofthe timing generator 111. In FIG. 30, a rounding section 117 roundsdigital data, which is inputted as data to be compressed, by using afirst value N₁ (division using a first value N₁). For example, therounding section 117 rounds inputted digital data by 8 or 16.

A differentiator 118 differentiates digital data, which is rounded bythe rounding section 117, for one time. At this moment, thedifferentiator 118 differentiates digital data every time an input clockCK of 44.1 KHz is supplied, that is, on each sampling point depending ona reference frequency. A differential value is determined by, forexample, subtracting current data, which is captured at timing of aninput clock CK, from data captured at timing of the previous clock.

Moreover, a sample point detecting section 119 detects as a sample pointa point where digital data has a differential value changing inpolarity, according to a differential value computed by thedifferentiator 118. For example, the sample point detecting section 119detects a point where a differential value changes in polarity frompositive to negative or negative to positive and a point where adifferential value is 0. And then, regarding a point where adifferential value changes in polarity from positive to negative ornegative to positive, a point just before polarity changes is detectedas a sample point. Meanwhile, regarding a point where a differentialvalue is 0, the point is detected as a sample point. Additionally, whentwo or more points appear successively with differential values of 0,for example, both ends thereof are detected as sample points.

A timing generating section 120 counts the number of clocks CK suppliedfrom when a sample point is detected to when the subsequent, samplepoint is detected. The timing generating section 120 outputs the numberas timing data T and outputs timing pulse TP indicative of timing ofdetected points on sample points. Moreover, the timing generatingsection 120 also generates and outputs various clocks including areading clock.

As described above, in the present embodiment, before digital data isdifferentiated to detect a sample point, a rounding operation isperformed on the digital data. Although the rounding operation is notalways necessary, it is more preferable to perform the operation.Namely, when original data is differentiated without being rounded,small noise components and unnecessary signal components in originaldata may be detected as sample points, resulting in lowercompressibility. Therefore, it is preferable to perform differentiationafter the rounding operation.

However, when a first value N₁ for rounding is too large, an inflectionpoint (peak point), on which a differential value originally changes inpolarity, of original data is flattened and a necessary point may not bedetected as a sample point. In this case, correct data cannot bereproduced on the expansion side. For this reason, as a first value N₁,it is necessary to select a suitable value, which is not too large ortoo small (first value N₁=8 or 16 is preferable).

FIG. 31 is a diagram showing a detailed example of the configuration ofthe part for generating the timing pulse TP.

In FIG. 31, a first D-type flip flop 121 samples and stores inputteddigital data to be compressed, according to a clock CK having areference frequency. A multiplier (or divider) 122 multiplies digitaldata, which is stored in the first D-type flip flop 121, by 1/N₁.

The digital data multiplied by the multiplier 122 by 1/N₁ is supplied tothe negative side of a subtracter 124, and the digital data is suppliedto the positive side of the subtracter 124 after being delayed by aclock CK in a second D-type flip flop 123. Thus, in the subtracter 124,a differential value is determined by subtracting current data capturedat timing of an input clock CK from data captured at previous timing.

In the present embodiment, a differential value itself is not necessaryand only polarity needs to be determined when a sample point isdetected. Hence, only a sign bit of differential data is outputted fromthe subtracter 124. The sign bit of differential data that is outputtedfrom the subtracter 124 is supplied to one of the input terminals of anEXNOR circuit 126 and is delayed by a clock CK in a third D-type flipflop 125. Thereafter, the bit is supplied to the other input terminal ofthe EXNOR circuit 126. Hence, the EXNOR circuit 126 detects a samplepoint where a differential value changes in polarity, and timing pulseTP is outputted as data indicative of the detected point.

The explanation will be continued as follows in accordance with FIG. 28again. The rounding section 113 rounds amplitude data, which isoutputted from the amplitude generator 112, by using a second value N₂,which is larger than the first value N₁ and outputs compressed amplitudedata. For example, the rounding section 113 rounds by 1024 amplitudedata of each sample point that is outputted from the amplitude generator112. Since amplitude data is rounded by 1024, a data length can beshortened by ten bits per word, thereby largely reducing an amount ofdata.

Further, the difference computing section 114 determines a differencebetween pieces of compressed amplitude data that are obtained by therounding section 113. For example, difference data is sequentiallyobtained by subtracting compressed amplitude data on the previous samplepoint from compressed amplitude data on a sample point. According to theexample of FIG. 29, the difference computing section 114 performsD1/1024−D0/1024, D2/1024−D1/1024, D3/1024−D2/1024, . . . (division by1024 is a rounding operation of the rounding section 113). Since adifference is computed thus, it is possible to further reduce individualdata values as compared with compressed amplitude data before adifference is determined, thereby further shortening a data length.

The encoder 115 forms a block of a pair of timing data, which isdetermined by the timing generator 111, and compressed amplitudedifference data, which is determined by the difference computing section114, and outputs the pair to a transmission line (not shown) or the datamemory 116 as serial compressed block data.

Namely, the encoder 115 forms a block of a pair of compressed amplitudedifference data and timing data by parallel/serial conversion, andoutputs the data block after adding a header and various flags to thefront of the data block. The header includes information such as anidentification mark of the header and a value N₁ used for rounding ofthe rounding section 117. An initial value of compressed amplitude dataand a data block, which is composed of a pair of compressed amplitudedifference data and timing data, follow the above header in ascendingorder. Here, a rounding value N₁ is included in the header because arounding value N₁ is changed to a suitable value for a signal to becompressed.

The data memory 116 is a record medium for storing compressed data. Thedata memory 116 captures and records serial compressed block datagenerated by the encoder 115, according to a clock transmitted from thetiming generator 111 via the encoder 115. Further, in response to areading clock supplied from the outside, stored compressed data is readand outputted.

FIG. 32 is a diagram for explaining an example of an actual compressionoperation performed by the compression apparatus shown in FIG. 28. Here,in FIG. 32, a vertical direction indicates the passage of time fromabove to below.

Of all data strings A to I of FIG. 32, the data string A on the leftmostside indicates raw data before compression. The raw data is sampledaccording to a sampling frequency of 44.1 KHz.

The second data string B from the left is the result of rounding rawdata by 16 in the rounding section 117 (the multiplier 122 of FIG. 31)of FIG. 30. The third data string C is the result of rounding raw databy 1024 in the rounding section 113 of FIG. 28.

The fourth data string D is the result of differentiating the seconddata string B (data obtained by rounding raw data by 16) in thedifferentiator 118 of FIG. 30. For example, the second differentialvalue “24” from above is determined by “696−672” using data of the datastring B, and the subsequent differential value “11” is determined by“707−696” using the subsequent data of the data string B.

The fifth data string E is a flag for indicating a point just before adifferential value changes in polarity from positive to negative ornegative to positive. Namely, “1” is set on a point just before adifferential value changes in polarity, and “0” is set on other points.For example, as for differential values on the fourth data string D, ona part where a differential value changes from “11” to “−47”, a flag “1”is set on a point of “11” just before a differential value changes inpolarity. Further, on a part where a differential value changes from“−15” to “20”, a flag “1” is set on a point of “−15” just before adifferential value changes in polarity. A point where a flag “1” is setserves as a sample point.

The sixth data string F indicates compressed amplitude data generated bythe rounding section 113 of FIG. 28. Here, for understanding ofcomparison with expansion, which will be discussed later, compressedamplitude data is shown on each point when oversampling is performed ata double frequency.

Actually, compressed amplitude data exists only on a sample point havinga flag “1” on the data string E. Compressed amplitude data exists in asimilar manner on the following data strings G to I as well.

The seventh data string G is compressed amplitude difference datagenerated by the difference computing section 114 of FIG. 28. Forexample, the highest data value “−1” is determined by “10−11” using datavalues on successive sample points of the data string F, and thesubsequent data value “0” is determined by “10−10” using data values onthe subsequent successive sample points of the data string F.

The eighth data string H indicates timing data generated by the timinggenerator 111 of FIG. 28. Here, the number of clocks CK is shown, whichare supplied from when a sample point is detected to when the subsequentsample point is detected. On this string as well, timing data is shownon each sampling point having a double frequency. Actually, timing dataexists only on sample points having flags “1”.

The ninth data string I has a flag showing a separation of data. Namely,when compressed amplitude data has the same values on successive samplepoints, flag values to “0” and “1” are set to indicate different samplepoints. For example, a value of compressed amplitude data is “10” bothon the second sample point and the third sample point of the data stringF. Thus, in order to indicate different sample points having equalcompressed amplitude data values, a data separating flag having adifferent value is set.

Of the above data strings, the encoder 115 forms a block of an initialvalue “11” of compressed amplitude data shown in the data string F and apair of (−1,2), (0,1), (−3,3), . . . , which are compressed amplitudedifferences and timing data on the sample points of the data strings Gand H, and the data block is outputted as serial compressed block data.

As described above, according to the compression apparatus of thepresent embodiment, the raw data to be compressed on the data string Acan be substantially compressed to data only on the sample points of thedata strings G and H. Additionally, data values on the sample points canbe compressed to extremely small values as compared with raw data.

FIGS. 33A and 33B are diagrams showing an example of the configurationof serial compressed block data according to the present embodiment. Inthe present embodiment, block data is variable-length data as will bediscussed below.

FIG. 33A shows a block structure of compressed amplitude differencedata. In FIG. 33A, the first bit is a data sign bit (sign bit)indicative of polarity of compressed amplitude difference data. Forexample, a value “1” of a data sign bit indicates a negative number anda value “0” indicates a positive number.

Further, the second bit is a separating flag indicative of the number ofbits of compressed amplitude difference data. For example, when theseparating flag has a value of “1”, compressed amplitude difference dataincludes the following two bits (third and fourth bits). When theseparating flag has a value of “0”, compressed amplitude difference dataincludes the following five bits (third to seventh bits). In this sense,the separating flag indicates a separating point from the subsequentdata block.

As shown in the data string G of FIG. 32, most of compressed amplitudedifference data can be represented by two bits except for sign bits.Therefore, the separating flag is set at “1” and a two-bit length isassigned for most of compressed amplitude difference data, and theseparating flag is set at “0” and a five-bit length is assigned forcompressed amplitude difference data that is not represented by twobits. When five bits are assigned at the maximum, it is possible torepresent all of compressed amplitude difference data.

Meanwhile, FIG. 33B shows a block structure of timing data. The blocksof the timing data follow the blocks of the compressed amplitudedifference data. In FIG. 33B, the first bit is a separating flagindicative of the number of bits of the timing data. For example, whenthe separating flag has a value of “1”, the timing data includessubsequent three bits (second to fourth bits), and when the separatingflag has a value of “0”, the timing data includes subsequent eight bits(second to ninth bits).

As shown in the data string H of FIG. 32, timing data is all composed ofpositive numbers, and most of the data can be represented by three bits.Therefore, the separating flag is set at “1” and a three-bit length isassigned for most of timing data, and the separating flag is set at “0”and an eight-bit length is assigned for timing data not beingrepresented by three bits. When eight bits are assigned at the maximum,all of timing data can be represented.

As described above, in the compression apparatus of the presentembodiment, generated compressed data is further transmitted or recordedas variable-length block data. Hence, compressibility can be furtherincreased by about 1.5 times, thereby achieving higher compressibility.For example, compressibility of 12 or more can be achieved for somekinds of music data on CD.

The following will discuss an decompression apparatus for theabove-mentioned compression apparatus. FIG. 34 is a block diagramshowing an example of the configuration of the decompression apparatusaccording to the present embodiment. As shown in FIG. 34, thedecompression apparatus of the present embodiment is constituted by aPLL (Phase Locked Loop) circuit 131, a data memory (option) 132, adecoder 133, a timing generator 134, and a square-law interpolation datagenerating section 135.

The PLL circuit 131 generates a clock 2CK having a double frequency(88.2 KHz) from an input clock CK having a reference frequency (44.1KHz) and supplies the clock 2CK to the timing generator 134 and thesquare-law interpolation data generating section 135. Moreover, the datamemory 132 is a record medium for storing serial compressed block datatransmitted from the compression apparatus.

The decoder 133 decodes serial compressed block data, which is read fromthe data memory 132, by using various clocks synchronized with a clock2CK having a double frequency, and takes out a pair of compressedamplitude difference data and timing data. And then, the takencompressed amplitude difference data is outputted to the square-lawinterpolation data generating section 135, and the taken timing data isoutputted to the timing generator 134 and the square-law interpolationdata generating section 135. Compressed amplitude difference data issynchronized with a frequency between sample points by performingsampling in the square-law interpolation data generating section 135according to a timing pulse TP.

The timing generator 134 generates a timing pulse TP, which isindicative of a time interval as irregular as sample points detected onthe compression side, from an input clock 2CK in response to timing datasupplied from the decoder 133. Moreover, the timing generator 134 alsogenerates and outputs various clocks including a reading clock for thedata memory 132.

The square-law interpolation data generating section 135 performs apredetermined square-law interpolating operation using compressedamplitude difference data and timing data that are inputted from thedecoder 133. Thus, digital interpolation data is generated forconnecting sample points. The details of the square-law interpolatingoperation will be discussed later. Interpolation data generated thus isa series of amplitude data that is generated by performing doubleoversampling on original data before compression. Digital interpolationdata generated thus is outputted as expansion data.

Besides, the example of FIG. 34 shows expansion of digital data.Obtained digital data may be converted to an analog signal as necessarybefore being outputted. In this case, for example, the output stage ofthe square-law interpolation data generating section 135 is providedwith a D/A converter and an LPF. Namely, after digital interpolationdata outputted from the square-law interpolation data generating section135 is converted to an analog signal by the D/A converter, the signal isoutputted as a reproduced analog signal via the LPF.

FIG. 35 is a diagram showing a detailed example of the configuration ofthe above square-law interpolation data generating section 135. In FIG.35, timing data (T) inputted as a part of compressed data is stored inthree D-type flip flops 143, 146, and 149 according to a timing pulseTP, which is sequentially supplied. Further, a clock 2CK having a doublefrequency is inputted to the first counter 141 and the number of theclocks is counted sequentially.

A first comparator 142 compares the number of clocks 2CK, which iscounted by a first counter 141, and timing data stored in the D-typeflip flop 143. And then, every time the number of counted clocks 2CKexceeds a timing data value, the comparator 142 outputs a signalindicative of the state (A>B). A second OR circuit 148 ORs a signaloutputted from the first comparator 142 and an external start signal,and outputs the result as a timing pulse TP.

Here, the second OR circuit 148 generates a timing pulse TP because atiming pulse TP needs to be reproduced only by the decompressionapparatus. In this case, when the second OR circuit 148 ORs an outputsignal of the first comparator 142 and an external start signal, atiming pulse TP can be obtained therefrom.

Further, a second counter 144 sequentially counts the number of clocksCK having a reference frequency. A second comparator 145 compares thenumber of clocks CK, which are counted by the second counter 144, andtiming data stored in the D-type flip flop 146. And then, every time thenumber of counted clocks CK exceeds a value of timing data, the secondcounter 144 outputs a signal indicative of the state. A first OR circuit147 ORs a signal outputted from the second comparator 145 and anexternal start signal, and outputs the result to an EXOR circuit 151.

As described above, when the number of clocks CK according to areference frequency and the number of clocks 2CK according to a doublefrequency are each compared with timing data and an OR is determinedusing signals of the comparison results, a conforming signal (A>B) isoutputted from the first OR circuit 147 just at an intermediate positionof a time interval between two sample points, the time interval beingindicated by timing data (position at a half number of clocks 2CKindicative of the time interval).

Meanwhile, compressed amplitude difference data inputted as a part ofcompressed data is stored in a D-type flip flop 152 according to atiming pulse TP, which is sequentially supplied. Compressed amplitudedifference data stored in the D-type flip flop 152 is supplied to afirst adder 154 after being oversampled by a D-type flip flop 153according to a clock 2CK having a double frequency.

The first adder 154 integrates compressed amplitude difference data byadding compressed amplitude difference data supplied from the D-typeflip flop 153 and accumulated data until then that is stored in a D-typeflip flop 155.

Upon integration, the first adder 154 reverses a sign of compressedamplitude difference data as necessary, which is inputted from theD-type flip flop 153, according to an output signal from the EXORcircuit 151. In addition to a conforming signal (A>B) outputted from theabove first OR circuit 147, a data sign bit (sign bit of FIG. 33), whichis stored in the D-type flip flop 152 according to a timing pulse TP, isinputted to the EXOR circuit 151.

Thus, the first adder 154 reverses a sign of compressed amplitudedifference data when a data sign bit included in a block data ofcompressed amplitude difference data or a conforming signal (A>B) fromthe first OR circuit 147 is reversed in value, that is, on sample pointsand just at an intermediate position between two sample points.

A first integral value of compressed amplitude difference data that isdetermined by the first adder 154 is supplied to a second adder 156. Thesecond adder 156 further integrates the first integral value by addingthe first integral of compressed amplitude difference data andaccumulated data until then. The first integral value is supplied fromthe first adder 154 and the accumulated data is stored in a D-type flipflop 157.

A second integral value of compressed amplitude difference data that isdetermined by the second adder 156 is directly inputted to one of theinput terminals of a third adder 159 and is inputted to the other inputterminal of the third adder 159 after being temporarily stored in aD-type flip flop 158. The third adder 159 carries out a moving averageoperation (convoluting operation) by adding a second integral value ofcompressed amplitude difference data and a value obtained by shiftingthe integral value by a clock 2CK, and the third adder 159 outputs theresult to a multiplier 160.

In the three D-type flip flops 155, 157, and 158, a value is reset at 0every time a timing pulse TP is supplied. The D-type flip flops 155 and157 constitute integrators of the first and second stages, and theD-type flip flop 158 shifts a second integral value by a clock 2CK.Hence, the second integration and the moving average operation ofcompressed amplitude difference data are separately carried out in eachperiod of a timing pulse TP (each section between sample points).

The multiplier 160 multiplies a moving average data value, which isdetermined by the third adder 159, by 512/T² (T represents timing data),and outputs the result to a fourth adder 161. The fourth adder 161 addsa data value from the multiplier 160 and a data value obtained bymultiplying an initial value (“11” in the example of FIG. 32) ofcompressed amplitude data by 1024 in another multiplier 162. And then,data outputted from the fourth adder 161 is outputted as expansion dataafter being temporarily stored in the D-type flip flop 162 according toa clock 2CK having a double frequency.

With the above configuration, after compressed amplitude difference datais integrated twice, a moving average operation of a first stage isperformed and the operation of the following equation (8) is performedon data M of the operating result.

(M/2T² +F)?1024=(M/T ²)?512+F?1024  (8)

Here, F represents a current value of compressed amplitude data. Thus,it is possible to realize a circuit for performing oversamplingsquare-law interpolation on sample points having irregular intervals(variable clock) without using a table.

FIG. 36 is a diagram for explaining an example of an actualdecompression operation performed by the decompression apparatus of FIG.34. Here, in FIG. 36, a vertical direction represents the passage oftime from above to below.

Of data strings A to G shown in FIG. 36, the data string A on theleftmost side includes data obtained by performing oversampling oncompressed amplitude difference data according to a clock 2CK having adouble frequency and reversing a sign with a half period of a timingpulse TP. For example, four data values (−1, −1, 1, 1) from above arereversed in sign at an intermediate position of four data values {−1,−1, −1, −1} of the data string G shown in FIG. 32.

The second data string B from the left includes data obtained byintegrating compressed amplitude difference data for one time in thefirst adder 154 of FIG. 35. For example, in the operation on the higheststage, an initial value “0” of the D-type flip flop 155 and a data value“−1” from the D-type flip flop 153 are added up to an accumulated value“−1” of the D-type flip flop 155. In the operation on the second stage,an accumulated value “−1” of the D-type flip flop 155 and a data value“−1” from the D-type flip flop 153 are added up to an accumulated value“−2” of the D-type flip flop 155. The same operation is performed on thethird and fourth stages, and the D-type flip flop 155 has accumulatedvalues “−1” and “0” in order.

The third data string C includes data obtained by integrating compressedamplitude difference data twice in the second adder 156 of FIG. 35. Forexample, in the operation on the highest stage, an initial value “0” ofthe D-type flip flop 157 and a data value “−1” from the first adder 154are added up to an accumulated value “−1” of the D-type flip flop 157.In the operation on the second stage, an accumulated value “−1” of theD-type flip flop 157 and a data value “−2” from the first adder 154 areadded up to an accumulated value “−3” of the D-type flip flop 157. Thesame operation is performed on the third and fourth stages, and theD-type flip flop 157 has accumulated values “−4” and “−4” in order.

The fourth data string D includes data obtained by shifting the thirddata string C by a clock 2CK in the D-type flip flop 158 of FIG. 35.Further, the fifth data string E includes data obtained by adding thethird data string C and the fourth data string D in the third adder 159of FIG. 35.

As described above, until the fifth data string E is obtained, thesecond integration and the moving average operation are separatelycarried out in each period of a timing pulse TP (each section betweensample points). Namely, the above operations are carried out in each ofthe sections divided by dotted lines of FIG. 36. Hence, digitalwaveforms are generated separately in the sections between samplepoints.

The sixth data string F includes expansion data generated by processingof the multiplier 160 and later of FIG. 35. Namely, since theinterpolating operation of equation (8) is performed on a digitalwaveform obtained thus for each of the sections between sample points, adigital waveform (oversampled interpolation data) is obtained forsmoothly connecting digital waveforms of the individual sections.

In the present embodiment, as shown in FIG. 29, inflection points (peakpoints) of a digital waveform are detected as sample points, data on thesample points is processed as compressed data. Therefore, compresseddata includes all minimum data required for reproducing original data byexpansion. Hence, data other than inflection points can be smoothlyinterpolated with 16-bit accuracy by performing square-law interpolationusing the compressed data.

Further, in the present embodiment, when double integration is performedon compressed amplitude difference data, compressed amplitude differencedata inputted to an integrator (first adder 154) of the first stage isreversed in sign at a half of a period between sample points. Thus, itis possible to obtain a digital waveform with amplitude values changingmore smoothly by integration and a moving average operation on thesubsequent second stage.

Moreover, in the present embodiment, when an operation such asintegration is performed, the D-type flip flop in an integrator and amoving average computing section on each stage are reset in value foreach timing pulse TP. Thus, it is possible to accurately conduct theoverall algorithm and to eliminate an accumulative error of theintegrator, thereby reproducing a more accurate digital waveform.

In this manner, the decompression apparatus of the present embodimentcan reproduce original data almost faithfully.

The seventh data string G of FIG. 36 includes data obtained byinterpolating original data before compression with a double frequency.As shown in comparison between original data on the data string G beforecompression and expansion data on the data string F, expansion datagenerated by the decompression apparatus of the present embodiment hassubstantially the same values as original data before compression.

FIG. 37 is a graph showing the data strings F and G. As shown in thegraph, the decompression apparatus of the present embodiment canreproduce substantially the same data as original data beforecompression.

As specifically described above, according to the present embodiment,digital data to be compressed can be compressed and expanded directly ona time base without time/frequency conversion. Thus, the operation isnot complicated and the configuration can be simplified. Further,without using table information, a simple interpolating operation on atime base can sequentially process and reproduce compressed data to beinputted, thereby realizing real-time operations.

Besides, in the present embodiment, a point where digital data has adifferential value changing in polarity is detected as a sample point,compressed data is generated from an amplitude data value on eachdetected sample point and a timing data value indicative of a timeinterval of sample points, and the compressed data is transmitted orrecorded. Hence, only data on a sample point can be obtained ascompressed data, thereby achieving high compressibility.

Further, in the present embodiment, amplitude data on each sample pointis not used as compressed data directly but is rounded by 1024. Hence, adata length can be shortened by several bits per word, thereby largelyreducing an amount of data. Furthermore, rounded amplitude data is notused as compressed data directly but difference data thereof is obtainedand is used as compressed data. Thus, the number of bits required forcompressed data can be further reduced, achieving a smaller amount ofdata.

Additionally, in the present embodiment, obtained compressed amplitudedifference data and timing data are encoded to variable-length blockdata and are used as final compressed data. Therefore, compressibilitycan be further improved by about 1.5 times, thereby achieving extremelyhigh compressibility.

Further, in the present embodiment, digital data is rounded by asuitable value before a differential value is determined for detecting asample point. Thus, it is possible to prevent noise components andunnecessary signal components from being detected as sample points andto positively detect only accurate positions as sample points. Moreover,during expansion, on the first stage of a double integrator, additionand subtraction are switched in the first half and the second half ofthe period of a timing pulse TP. Thus, it is possible to compensate fora rounding error on the expansion side and to reproduce a digitalwaveform having amplitude values changing more smoothly.

Also, in the present embodiment, when an operation such as doubleintegration is performed together with oversampling, an accumulatedvalue of the integrator on each stage is reset in each timing pulse TP.Hence, it is possible to eliminate an accumulative error of theintegrator and to reproduce a more accurate digital waveform. Thus, itis possible to obtain high-quality expansion data close to original databefore compression.

As described above, according to the compression and decompressionmethods of the present embodiment, it is possible to provide newcompression and decompression methods for realizing extremely highcompressibility and higher quality of reproduced data.

Besides, the above Embodiment 3 describes the example in which therounding section 113 rounds an amplitude data value by 1024. However,the value is not limited to 1024.

Moreover, although double oversampling is performed in the aboveEmbodiment 3, oversampling is not limited to double as long as it isperformed by even-numbered times.

Additionally, in Embodiment 3, during compression, amplitude data onsample points is extracted from digital data inputted to be compressed,and then, the extracted amplitude data is rounded by a second value N₂.Compressed amplitude data on sample points may be extracted afterinputted digital data is rounded.

Further, in Embodiment 3, during expansion, double integration isperformed and a moving average operation of a single stage is performed.Integration is not limited to double and multiple integration is alsoapplicable. Besides, a moving average operation is not limited to asingle stage.

A moving average operation or a convoluting operation may be performedwith more stages.

Moreover, it is also possible to combine the compression anddecompression methods of the above Embodiments 1 to 3 as necessary or tointerchange constituent technologies as necessary. For example,Embodiments 1 to 3 describes three different methods of detecting asample point. Any one of the detecting methods is applicable in theembodiments.

The above-mentioned compression and decompression methods of Embodiments1 to 3 can be realized by any of hardware, DSP, and software. Forexample, in the case of software, the compression apparatus and thedecompression apparatus of the present embodiments are actually composedof a CPU or MPU, RAM, ROM, and so on of a computer, and the methods arerealized by operating programs stored in a RAM and ROM.

Therefore, the methods are realized as follows: programs for operating acomputer for achieving the function of the present embodiments arestored in a record medium such as a CD-ROM, and the programs are read bythe computer. As a record medium for recording such programs, a floppydisk, a hard disk, a magnetic tape, an optical disk, a magneto-opticaldisk, a DVD, a nonvolatile memory card, and so on are applicable inaddition to a CD-ROM. Further, the methods can also be realized bydownloading the programs to a computer via a network such as theInternet.

Further, the computer runs supplied programs to achieve the function ofthe above embodiments. Additionally, the embodiments of the presentinvention also include the programs used in the case where the programsrealize the function of the above embodiments in coordination with an OS(operating system), which operates in the computer, or other applicationsoftware and the like, and the case where all or some of the operationsof the supplied programs are performed by a function extended board anda function extended unit of the computer to achieve the function of theabove embodiments.

Additionally, each of the above-mentioned embodiments merely shows aspecific example for realizing the present invention. It should beunderstood that the present invention is not interpreted within alimited technical range. Namely, the present invention is to covervarious forms within the spirit or major characteristics of theinvention.

[Industrial Applicability]

The present invention is useful for providing new compression anddecompression methods capable of realizing both of extremely highcompressibility and higher quality of reproduced data with a simpleconfiguration and in a shorter compression and decompression time.

What is claimed is:
 1. A compression method characterized in that asignal to be compressed is sampled at a time interval of a point where adifferential absolute value is at a predetermined value or smaller, anda pair of discrete amplitude data on each sample point and timing dataindicative of the time interval between sample points is obtained ascompressed data.
 2. A record medium being capable of computer reading,characterized by recording a program for causing a computer to carry outthe steps of said compression method according to in claim
 1. 3. Acompression method characterized in that a signal to be compressed isoversampled, said oversampled data is sampled at a time interval of apoint where a differential absolute value is at a predetermined value orsmaller, and a pair of discrete amplitude data on each sample point andtiming data indicative of the time interval between sample points isobtained as compressed data.
 4. The compression method according toclaim 3, said oversampled data is further subjected to an operation forgenerating average value data of successive sample values.
 5. Acompression apparatus, comprising: differentiating means fordifferentiating digital data to be compressed, sample point detectingmeans for detecting a sample point where a differential absolute valuedetermined by said differentiating means is at a predetermined value orsmaller, and compression means for outputting as compressed data a pairof amplitude data on a sample point detected by said sample pointdetecting means and timing data indicative of a time interval betweensample points.
 6. The compression apparatus according to claim 5,further comprising A/D converting means for generating said digital datato be compressed by performing A/D conversion on an inputted analogsignal.
 7. The compression apparatus according to claim 5, furthercomprising oversampling means for oversampling said digital data to becompressed by using a clock having a frequency of even-numbered times,said differentiating means differentiates digital data generated by saidoversampling means, and said compression means outputs timing datameasured according to the clock having said frequency of even-numberedtimes.
 8. The compression apparatus according to claim 7, furthercomprising average value data generating means for generating averagevalue data of successive sample values for digital data generated bysaid oversampling means, said differentiating means differentiatesdigital data generated by said average value data generating means. 9.An decompression method characterized in that regarding compressed datacomposed of a pair of amplitude data on predetermined sample pointsextracted from a signal to be compressed and timing data indicative of atime interval between sample points, amplitude data on successive samplepoints and timing data therebetween are used to obtain expansion data bydetermining interpolation data for interpolating pieces of amplitudedata having a time interval indicated by said timing data.
 10. Thedecompression method according to claim 9, a sampling function obtainedfrom two pieces of amplitude data on two successive sample points andtiming data therebetween is used to obtain interpolation data forinterpolating said two pieces of amplitude data.
 11. A record mediumbeing capable of computer reading, characterized by recording a programfor causing a computer to carry out the steps of said decompressionmethod discussed in claim
 9. 12. An decompression apparatus, comprising:timing control means for controlling timing such that amplitude data oneach sample point that is included in compressed data is sequentiallycaptured at each time interval between said sample points according totiming data indicative of a time interval between said sample pointsextracted from a signal to be compressed, said timing data beingincluded in said compressed data, and decompression means for obtainingexpansion data by determining interpolation data for interpolating twopieces of amplitude data by using said two pieces of amplitude data ontwo successive sample points and timing data therebetween, saidamplitude data being captured under control of said timing controlmeans.
 13. The decompression apparatus according to claim 12, saiddecompression means uses a sampling function obtained from two pieces ofamplitude data on said two successive sample points and timing datatherebetween so as to obtain interpolation data for interpolating saidtwo pieces of amplitude data.
 14. A compression method characterized inthat digital data of a basic waveform corresponding to values ofinputted n pieces of discrete data is synthesized by oversampling and amoving average operation or a convoluting operation so as to obtaindigital interpolation values for said discrete data, and then, saiddetermined digital interpolation values are sampled at a time intervalof a point having a minimum differential absolute value, and a pair ofdiscrete amplitude data on sample points and timing data indicative ofthe time interval between sample points is obtained as compressed data.15. A record medium being capable of computer reading, characterized byrecording a program for causing a computer to carry out the steps ofsaid compression method according to claim
 14. 16. A compressionapparatus, comprising: oversampling means for determining a digitalinterpolation value for discrete data by synthesizing digital data of abasic waveform corresponding to values of inputted n pieces of discretedata by oversampling and a moving average operation or a convolutingoperation, differentiating means for differentiating a digitalinterpolation value determined by said oversampling means, andcompressed data generating means for detecting a sample point having aminimum differential value determined by said differentiating means andoutputting as compressed data a pair of amplitude data on detectedsample points and timing data indicative of a time interval betweensample points.
 17. The compression apparatus according to claim 16,further comprising rounding means for rounding a lower-order bit of adifferential absolute value determined by said differentiating means,said compressed data generating means detects as the sample point apoint having a minimum differential absolute value rounded by saidrounding means.
 18. The compression apparatus according to claim 16,said compressed data generating means detects as the sample point only apoint where a differential absolute value is below a fixed value, frompoints having a minimum differential absolute value determined by saiddifferentiating means or a minimum differential absolute value roundedby said rounding means.
 19. The compression apparatus according to claim16, said oversampling means performs oversampling on the digital data ofthe basic waveform corresponding to values of said inputted n pieces ofdiscrete data, by using a clock having a frequency of an integralmultiple, and said compressed data generating means outputs timing datameasured according to the clock having said frequency of the integralmultiple.
 20. The compression apparatus according to claim 16, saidoversampling means comprising; storing means for storing in advance dataobtained by oversampling digital data of said basic waveform, andperforming the moving average operation or the convoluting operation onoversampled data of a basic waveform, and synthesizing means formodulating data stored in said storing means to amplitude correspondingto values of said inputted n pieces of discrete data and synthesizes npieces of data obtained thus by the moving average operation orconvoluting operation.
 21. A record medium being capable of computerreading, characterized by recording a program for causing a computer tofunction as said means according to claim
 16. 22. Acompression/decompression system characterized in that on a compressionside, a signal to be compressed is sampled at a time interval of a pointwhere a differential absolute value is at a predetermined value orsmaller, and a pair of discrete amplitude data on each sample point andtiming data indicative of the time interval between sample points isobtained as compressed data, and on an expansion side, amplitude dataand timing data that are included in said compressed data are used toreproduce said amplitude data so as to have the time interval indicatedby said timing data, and expansion data is obtained by determininginterpolation data based on two pieces of amplitude data on twosuccessive sample points and timing data therebetween, saidinterpolation data interpolating said two pieces of amplitude data. 23.A compression apparatus, comprising: oversampling means for determininga digital interpolation value for discrete data by synthesizing digitaldata of a basic waveform corresponding to values of inputted n pieces ofdiscrete data by oversampling and a moving average operation or aconvoluting operation, first differentiating means for determining adifferential absolute value by differentiating a digital interpolationvalue determined by said oversampling means, second differentiatingmeans for determining a double differential value by furtherdifferentiating a differential absolute value obtained by said firstdifferentiating means, sample point detecting means for detecting apoint where a double differential value determined by said seconddifferentiating means changes in polarity from negative or 0 to positiveas a sample point having a minimum differential absolute valuedetermined by said first differentiating means, and compressed datagenerating means for outputting as compressed data a pair of amplitudedata on sample points detected by said sample point detecting means andtiming data indicative of a time interval between sample points.
 24. Thecompression apparatus according to claim 23, said sample point detectingmeans detects as said sample point points where the double differentialvalue determined by said second differentiating means changes inpolarity from negative or 0 to positive and the differential absolutevalue determined by said first differentiating means is below a fixedvalue.
 25. The compression apparatus according to claim 23, furthercomprising rounding means for rounding a lower-order bit of thedifferential absolute value determined by said first differentiatingmeans, said second differentiating means further differentiates thedifferential absolute value rounded by said rounding means.
 26. Thecompression apparatus according to claim 25, said sample point detectingmeans detects as said sample point a point where the differentialabsolute value rounded by said rounding means is below a fixed value,from the points where the double differential value determined by saidsecond differentiating means changes in polarity from negative or 0 topositive.
 27. A compression/decompression system characterized in thaton a compression side, digital data of a basic waveform corresponding tovalues of inputted n pieces of discrete data is synthesized byoversampling and a moving average operation or a convoluting operationso as to obtain a digital interpolation value for said discrete data,and then, said obtained digital interpolation value is sampled at a timeinterval of a point having a minimum differential absolute value, a pairof discrete amplitude data on each sample point and timing dataindicative of the time interval between sample points is obtained ascompressed data, and on an expansion side, amplitude data and timingdata that are included in said compressed data are used to obtainexpansion data by determining interpolation data for interpolating twopieces of amplitude data based on said two pieces of amplitude data ontwo successive sample points and timing data therebetween.
 28. Thecompression/decompression system according to claim 27, oversampling isperformed on digital data of the basic waveform corresponding to valuesof said inputted n pieces of discrete data by using a clock having afrequency of an integral multiple, and timing data is outputted, whichis measured according to the clock having said frequency of the integralmultiple.
 29. The compression/decompression system according to claim27, a sampling function with a definite base is used to determineinterpolation data for interpolating two pieces of amplitude data, saidsampling function being obtained from two pieces of amplitude data onsaid two successive sample points and timing data therebetween.
 30. Arecord medium being capable of computer reading, characterized byrecording a program for causing a computer to realize the function ofsaid compression/decompression system according to claim
 27. 31. Acompression method characterized in that inputted digital data isdifferentiated, a point where a differential value changes in polarityis detected as a sample point, digital data rounded by a predeterminedvalue is obtained as discrete compressed amplitude data on each samplepoint, and a pair of compressed amplitude difference data, which isobtained by computing a difference between pieces of said compressedamplitude data, and timing data indicative of a time interval betweensample points is obtained as compressed data.
 32. The compression methodaccording to claim 31, inputted digital data is rounded by a firstvalue, digital data rounded by said first value is differentiated, apoint where a differential value changes in polarity is detected as asample point, and digital data rounded by a second value, which islarger than said first value, is obtained as discrete compressedamplitude data on each sample point.
 33. The compression methodaccording to claim 31, said compressed amplitude difference data andsaid timing data are converted to variable-length block data.
 34. Thecompression method according to claim 33, a single variable-length blockof said compressed amplitude difference data is composed of a sign bitindicative of polarity of said compressed amplitude difference data, aseparating flag indicative of a bit length of said compressed amplitudedifference data, and said compressed amplitude difference data having abit length indicated by said separating flag.
 35. The compression methodaccording to claim 33, the single variable-length block of said timingdata is composed of a separating flag indicative of a bit length of saidtiming data, and said timing data having a bit length indicated by saidseparating flag.
 36. A record medium being capable of computer reading,characterized by recording a program for causing a computer to carry outthe steps of said compression method according to claim
 31. 37. Acompression apparatus, comprising: timing data generating means fordifferentiating inputted digital data, detecting a point having adifferential value changing in polarity as a sample point, and obtainingtiming data indicative of a time interval between sample points,compressed amplitude data generating means for generating data obtainedby rounding said inputted digital data by a predetermined value asdiscrete compressed amplitude data on each sample point detected by saidtiming data generating means, and difference computing means forcomputing a difference between pieces of compressed amplitude dataobtained by said compressed amplitude data generating means, a pair ofcompressed amplitude difference data obtained by said differencecomputing means and timing data obtained by said timing data generatingmeans is obtained as compressed data.
 38. The compression apparatusaccording to claim 37, further comprising first rounding means forrounding said inputted digital data by a first value, said timing datagenerating means differentiates digital data rounded by said firstrounding means and detects as the sample point a point having thedifferential value changing in polarity, and said compressed amplitudedata generating means generates said compressed amplitude data byrounding said digital data by a second value larger than said firstvalue.
 39. The compression apparatus according to claim 37, saidcompressed amplitude data generating means comprising; amplitude dataextracting means for extracting digital data on each sample point, whichis detected by said timing data generating means, as discrete amplitudedata, and second rounding means for rounding amplitude data extracted bysaid amplitude data extracting means by a second value.
 40. Thecompression apparatus according to claim 37, further comprising encodingmeans for converting said compressed amplitude difference data and saidtiming data to variable-length block data.
 41. The compression apparatusaccording to claim 40, a single variable-length block of said compressedamplitude difference data is composed of a sign bit indicative ofpolarity of said compressed amplitude difference data, a separating flagindicative of a bit length of said compressed amplitude difference data,and said compressed amplitude difference data having a bit lengthindicated by said separating flag.
 42. The compression apparatusaccording to claim 40, a single variable-length block of said timingdata is composed of a separating flag indicative of a bit length of saidtiming data, and said timing data having a bit length indicated by saidseparating flag.
 43. A record medium being capable of computer reading,characterized by recording a program for causing a computer to functionas said means according to claim
 37. 44. An decompression methodcharacterized in that regarding compressed data composed of a pair ofcompressed amplitude difference data on predetermined sample points,which are extracted from digital data to be compressed, and timing dataindicative of a time interval between sample points, said compressedamplitude difference data oversampled by even-numbered times issubjected to multiple integral, a moving average operation is performedon an integral value, a moving average operating value obtained thus andsaid timing data are used to obtain as expansion data square-lawinterpolation data for interpolating pieces of amplitude data on samplepoints having a time interval indicated by said timing data.
 45. Thedecompression method according to claim 44, said compressed amplitudedifference data oversampled by even-numbered times is reversed in signat an intermediate position of each section between sample points, thesection being indicated by the timing data, and data strings obtainedthus are subjected to multiple integral.
 46. The decompression methodaccording to claim 44, said compressed amplitude difference dataoversampled by even-numbered times, multiple integral and the movingaverage operation are performed in each section between sample pointsindicated by said timing data.
 47. A record medium being capable ofcomputer reading, characterized by recording a program for causing acomputer to carry out the steps of said decompression method accordingto claim
 44. 48. An decompression apparatus, regarding compressed datacomposed of a pair of compressed amplitude difference data on apredetermined sample points extracted from digital data to be compressedand timing data indicative of a time interval between sample points,said decompression apparatus comprising: integrating means forperforming multiple integral on said compressed amplitude differencedata oversampled by even-numbered times, moving average computing meansfor performing moving average operation on an integral value computed bysaid integrating means, and interpolation data generating means forobtaining square-law interpolation data, which interpolates pieces ofamplitude data on sample points having a time interval indicated by saidtiming data, as expansion data by using a moving average operating valuecomputed by said moving average operating means and said timing data.49. The decompression apparatus according to claim 48, said integratingmeans comprises a sign reversing means of reversing a sign of saidcompressed amplitude difference data over sampled by said even-numberedtimes at an intermediate position of each section between sample pointsindicated by said timing data, on a first stage of said multipleintegral.
 50. The decompression apparatus according to claim 48, saidintegrating means comprises reset means of resetting an integral valueof said compressed amplitude difference data, which is oversampled bysaid even-numbered times, in each section between sample pointsindicated by said timing data.
 51. The decompression apparatus accordingto claim 48, said moving average computing means comprises reset meansof resetting a moving average operating value of the integral value,which is computed by said integrating means, in each section betweensample points indicated by said timing data.
 52. A record medium beingcapable of computer reading, characterized by recording a program forcausing a computer to function as said means according to claim 48.